The people who should be most committed to obeying the commands of Allaah and heeding His prohibitions are those whom He has blessed with guidance, knowledge of Islam and following the path of religious commitment, so how can people like these friends whom you describe as being religiously committed agree to follow in the footsteps of the shaytaan by doing that which Allaah has forbidden? Should they not be grateful for the blessing that Allaah has bestowed upon them by guiding them to Islam and religious commitment, so they should be the best examples of righteousness to others? 

As for the fact that these friends of yours know that they are doing something haraam, that counts for nothing here. Who says that mere knowledge is what prevents a person from falling into sin? Didn’t Iblees know that what his Lord enjoined upon him was true? Didn’t the Jews know that the Prophet was true? And so on and so forth. Allaah, may He be exalted, says (interpretation of the meaning): 

“Do they not travel in the land, and see what was the end of those before them? They were superior to them in strength, and they tilled the earth and populated it in greater numbers than these (pagans) have done, and there came to them their Messengers with clear proofs. Surely, Allaah wronged them not, but they used to wrong themselves”

[al-Room 30:9] 

“And they belied them (those Ayaat) wrongfully and arrogantly, though their ownselves were convinced thereof [i.e. those (Ayaat) are from Allaah, and Moosa (Moses) is the Messenger of Allaah in truth, but they disliked to obey Moosa (Moses), and hated to believe in his Message of Monotheism]. So see what was the end of the Mufsidoon (disbelievers, and disobedient to Allaah, evildoers liars)”

[al-Naml 27:14]

But the point here is that the one who knows, and exhorts others, and speaks, bears a greater responsibility, and his going against the knowledge that he has is worse and more reprehensible. 

Allaah says (interpretation of the meaning): 

“Enjoin you Al-Birr (piety and righteousness and each and every act of obedience to Allaah) on the people and you forget (to practise it) yourselves, while you recite the Scripture! Have you then no sense?”

[al-Baqarah 2:44] 

“O you who believe! Why do you say that which you do not do?

3. Most hateful it is with Allaah that you say that which you do not do”

[al-Saff 61:2-3]

What you must do is remind your friends of their duties, as Allaah says (interpretation of the meaning): 

“Therefore remind (men) in case the reminder profits (them).

10. The reminder will be received by him who fears (Allaah)”

[al-A’la 87:9-10] 

“Verily, those who are Al-Muttaqoon (the pious), when an evil thought comes to them from Shaytaan (Satan), they remember (Allaah), and (indeed) they then see (aright)”

[al-A’raaf 7:201]

Remind them that this is abhorrent for any Muslim, male or female, so how about if the Muslim woman is one who outwardly makes a display of commitment to the religion of Allaah, and sets an example for people, and calls people to Allaah?  

In Saheeh al-Bukhaari (3267) and Saheeh Muslim (2989) it is narrated that Usaamah ibn Zayd (may Allaah be pleased with him) said: I heard the Messenger of Allaah (peace and blessings of Allaah be upon him) say: “A man will be brought on the Day of Resurrection and thrown into the Fire; his intestines will spill forth and he will go around them as a donkey goes around the millstone. The people of Hell will gather around him and will say: O So and so, what is the matter with you? Did you not enjoin what is good and forbid what is evil? He will say: Yes, but I used to enjoin good and not do it, and I used to forbid evil and do it.” 

And it is narrated that the Prophet (peace and blessings of Allaah be upon him) said: “The likeness of a scholar who teaches good to the people but forgets about himself is that of a lamp that illuminates the people but burns itself.” Narrated by al-Khateeb in Iqtida’ al-‘Ilm (49) and elsewhere; classed as saheeh by al-Albaani in Saheeh al-Jaami’ no. 5831. 

‘Abd-Allaah ibn al-Mubaarak (may Allaah have mercy on him) said: 

I have seen sins deaden hearts and persisting in them may lead to humiliation

Forsaking sin brings life to the heart and it is better for your soul to go against whims and desires

Does anything corrupt the religion more than kings and bad priests and monks

Who sell their souls but did not make any gain and did not sell them for the right price

Because they are like one that feeds upon a corpse and every wise man knows such as one is a loser. 

As for the excuse of emotional attachment towards the boyfriend, this is the essence of whims and desires which lead one to doom, Allaah forbid. Allaah says (interpretation of the meaning): 

“Have you seen him who takes his own lust (vain desires) as his ilaah (god)? And Allaah knowing (him as such), left him astray, and sealed his hearing and his heart, and put a cover on his sight. Who then will guide him after Allaah? Will you not then remember?”

[al-Jaathiyah 45:23]

Qataadah (may Allaah have mercy on him) said: He does not feel attracted to anything but it will control him, because he does not fear Allaah. Tafseer al-Tabari (22/76). 

Allaah describes chaste believing women as those who avoid having boyfriends. He says (interpretation of the meaning): 

“And whoever of you have not the means wherewith to wed free believing women, they may wed believing girls from among those (slaves) whom your right hands possess, and Allaah has full knowledge about your Faith; you are one from another. Wed them with the permission of their own folk (guardians, Awliyaa’ or masters) and give them their Mahr according to what is reasonable; they (the above said slave-girls) should be chaste, not committing illegal sex, nor taking boyfriends”

[al-Nisa’ 4:25]

Al-musaafihaat (translated here as “committing illegal sex”) means women who fornicate or commit adultery, who commit immoral actions. As for taking boyfriends, this refers to women who make friends with men and take them as close friends, as Ibn ‘Abbaas and others among the salaf said. [See: Tafseer Ibn Katheer, 2/261]. 

By the same token, Allaah describes the chaste men who seek what is permissible and good. He says (interpretation of the meaning): 

“Made lawful to you this day are At‑Tayyibaat [all kinds of Halaal (lawful) foods, which Allaah has made lawful (meat of slaughtered eatable animals, milk products, fats, vegetables and fruits)]. The food (slaughtered cattle, eatable animals) of the people of the Scripture (Jews and Christians) is lawful to you and yours is lawful to them. (Lawful to you in marriage) are chaste women from the believers and chaste women from those who were given the Scripture (Jews and Christians) before your time when you have given their due Mahr (bridal-money given by the husband to his wife at the time of marriage), desiring chastity (i.e. taking them in legal wedlock) not committing illegal sexual intercourse, nor taking them as girlfriends. And whosoever disbelieves in Faith, [i.e. in the Oneness of Allaah and in all the other Articles of Faith i.e. His (Allaah’s) Angels, His Holy Books, His Messengers, the Day of Resurrection and Al‑Qadar (Divine Preordainments)], then fruitless is his work; and in the Hereafter he will be among the losers”

[al-Maa’idah 5:5]

Ibn Katheer (may Allaah have mercy on him) said: Just as He stipulated that women should be chaste, He also stipulated the same for men, which means that men should also be chaste. Hence He says “not committing illegal sexual intercourse”, which refers to those who commit fornication or adultery, who would not refrain from any sin and would indulge in sin whenever the opportunity arises, “nor taking them as girlfriends,” i.e., mistresses with whom they satisfy their sexual desires. End quote. 

Tafseer Ibn Katheer (3/43) 

For more information on the seriousness of these types of haraam relationships, and the attitude of Islam towards them, please see the answers to questions no. 59907, 47405, 36618, and many answers in the section on morals and manners. 

And Allaah knows best.