He bought a house with a riba-based loan; should she accept him as a husband?
The fact that you hate riba and refuse to marry someone who deals in it is something for which you deserve to be praised and appreciated. We ask Allaah to increase you in faith, knowledge and piety.
Taking out riba-based loans is emphatically forbidden, because of the stern warning that has been issued concerning riba, as Allaah says (interpretation of the meaning):
“O you who believe! Be afraid of Allaah and give up what remains (due to you) from Ribaa (from now onward) if you are (really) believers.
279. And if you do not do it, then take a notice of war from Allaah and His Messenger but if you repent, you shall have your capital sums. Deal not unjustly (by asking more than your capital sums), and you shall not be dealt with unjustly (by receiving less than your capital sums)”
Muslim narrated (1598) that Jaabir (may Allaah be pleased with him) said: The Messenger of Allaah (peace and blessings of Allaah be upon him) cursed the one who consumes riba and the one who pays it, the one who writes it down and the two who witness it, and he said: they are all the same.
This kind of borrowing is haraam, even if it is to buy a house. See the answer to question no. 21914 and 22905.
If this young man is acceptable in terms of religious commitment and character, then pray istikhaarah, asking Allaah for guidance, and accept his proposal of marriage. There is no sin on you for that, for no soul is made to bear the burden (of sin) of another. As for him, he has to repent to Allaah and resolve not to do that again in the future. We hope that Allaah will forgive him, because he did that on the basis of the opinion of a number of scholars, as you said, but the correct view is what we have mentioned. Buying a house is not one of the necessities that makes riba permissible, and the need for shelter may be met in other ways, such as renting a suitable house.
May Allaah help us and you to do that which He loves and which pleases Him.
And Allaah knows best.