I might be overacting but this is truly what I'm feeling right now.

I just recently learned that my partner had nearly or probably had sex with one of his close friend. Though it was from his past and it felt so heavy learning about it. The fact that it took him months before telling me this information. I don't have any problem with him being physically active in his past because before our relationship started I've already learned most of it. Basically even with that past I still learned how to love him. I accepted that version of him. It kinda sting knowing that he's been with women before (even though it's more on physical most of the time and not emotionl) but that's life and it's normal. It's his pass and I just learned to accept it slowly as I can. Also I accepted it a little better because I've known all of it even before I fall in love with him. Basically we were friends before we became lovers. But the recent information I learned caught me off guard especially how casually told me about it. This time it's different. We were in relationship when I found out. And the most awful thing is that the one girl he nearly get physical with and I think he did develop some feelings towards her at that time is one of her close friend. I feel awful, I hate feeling like this, I hate hating him. I hate feeling like this, I love him so much that it always hurts me when I hate him. Please help me I don't know what to do.