found out husbands elaborate sexual history on note app

My husband wrote in his cell phone all of his sexual history in a note app. The note was open on that page when I picked up the phone. The reason why I know what kind of list it was is because there were explicit descriptions of people/positions and I also recognised a few of the names of his ex girlfriends. My husband has been with married women, one night stands ( no names) had threesomes with a male friend of his, who he still keeps in contact and I know him. ( I can't look at his friend the same way now), and much, much more. His list was quite long and extensive it surprised me. I had no idea that my husband had such an elaborate sexual past. He never told me about it or rather never divulged much information about his past relationships. Our sex life was great before we got married and then right after our marriage, it just started to get stagnant. (That's also a work in progress.)

He wrote this note on the same day of his birthday this year. We've been married a little over a year and I took him out on that same day to celebrate his birthday. He was acting a little sad and keep on saying that he needed to lose weight. Nothing out of the ordinary, sure we all can afford to lose a little weight and thinking that he was a year older maybe he felt that he was getting old, but now I can't help but think that he was thinking of his past when he said that.

I'm not sure what to feel. I'm not jealous and I understand that it's his past which has nothing to do with me, we all have a history, but why write the names/details down now?? I got rid off my past when I married my husband and never looked back.

Kind of hurts...Very confused...