Sukuna didn't believe in love.
He also did not like permanent relationships, claiming that being attached to one person was boring and enslaving. So he kept his relationships on a casual level, just having fun.
It was easier that way, wasn't it?
But his whole worldview completely collapsed when he met you in college.
On the surface, you weren't his type at all. Just another ordinary girl. But somehow he started noticing you more and more, learning about the details of your personality that attracted him to you. And, horror of horrors, making him fall in love with you.
But of course, he was afraid to confess his feelings. After all, it had a poor reputation among women who weren't looking for one-time fun. He was also considered a bad person.
However, he couldn't give up the thought of something more. He wanted to know the feeling of your skin against his, the softness of your lips, and every curve and dip of your body. That's why he decided to offer you to be friends with benefits.
As stupid as it may have seemed, it was his pathetic attempt to get closer to the person who had turned his entire life upside down.
And surprisingly, despite your personality, you agreed. Maybe because you wanted to have some fun and gain experience. Anyway, Sukuna didn't think long about your reason
So now he met you regularly, just to feel your closeness for a few moments, to breathe in your scent. Pretend that you are more than just friends with benefits.
Even if it was painful for him.