I doubt that you can simply help someone who treated you like shit. At the same time, providing abnormal help puts you at a disadvantage if someone tries to take advantage of you. Empathy is good, but it's time to face reality. By providing such abnormal help, you put yourself at a disadvantage, which is something only a fool would do. But the main character is a good student, knows how to clean up, and has a part-time job in the service industry, which requires communication skills. The author has written the character terribly, so that he does things that are not characteristic of him.
Where are the minor inconveniences? He gives the key to the apartment to a person he hasn't seen in a long time, and on top of that, this person has a negative attitude toward the main character. What's more, he says he'll sleep in an internet café, which is not a minor inconvenience at all, knowing that a stranger will be in your apartment, and here it is important to clarify that this person, again, had a bad attitude towards the main character. In exchange, the main character gets nothing at all except a huge risk.
Again, what's in it for the main character? Why should he help someone who treated him like crap, only to get a huge risk in return? What can she give him? She's not a virgin, she doesn't have money, she doesn't have a college degree, and the main character can handle the housework himself and make enough money to support himself. As for why he should be afraid of the girl's boyfriend, the answer is simple. The girl's boyfriend had the courage to make her fall in love with him, while the main character puts himself in an unjustifiably risky position for no reason. The difference in their actions clearly shows the superiority of one over the other.
I also think that romance doesn't fit here. It would be much better to create a oneshot where the main character gets what he deserves for taking such a huge risk.
I say she is stupid not because she lacks education, but because she has put herself in such a terrible position. A smart person would never put themselves in such a position, but would try to prevent it in every possible way.
Personally, I think that you shouldn't help someone who treated you like shit. Especially if it puts you in danger.