Im a horrible person

My male bestfriend, that i was once in a relationship with has a girlfriend. I invited him over to my house to hang out one night. All was well, but things escalated and we ended up getting intimate. I feel so disgusting and horrible that this has happened. Its not fair for him or me or his girlfriend. He did not pressure me into anything i did the wrong thing by seducing him.

He isnt happy, and doesnt want to be in a committed relationship with her. But this isnt right. He is so lost and sad and confused with what he wants.

I know i have done the wrong thing. What can I do to help myself understand this situation. I feel disgusting, i feel sad, I hate myself for what has happened