Guarantee

So last night I went to see Mark. And It was all good fun until right before I left.
Now.. It was all because of his ex-girlfriend who he dated for four years, and I mean, I've known about her and have heard about her a lot before, and why he was with her and why he hated it and what she was like and yada ya. But yesterday he made something clear to me that set me over the edge.
Now... A lot of the time when he talks to me about her, he mentions that she never like... NEVER wanted to sleep with him, and made him feel like a bad person for even wanting to. Which is one of the reasons he cheated on her.
And, I knew this and I've freaked out about him cheating on her, but he knows it was a mistake and I mean, to a certain extent I can kind of understand why he'd want to find validation, almost, through someone else. Its not awesome to me, He shouldn't have done it, but its in his past and I was giving him the benefit of the doubt.
But he made it seem like with his ex, she NEVER put out, like... he would go months on end without getting any. I can also understand where that would be frustrating. Living with someone, having dated them for four years and never like... EVER having sex.
But last night, he was talking about something, and that whole thing came up, and he said something like it would be a maximum of two days that she wouldn't sleep with him.
It took a minute to register what he'd said, but I was stunned.
"Two days?" I'd said.
And he kind of laughed and said "Yeah" and started comparing it to something else but I stopped him. I wouldn't listen anymore.
I flipped.
I straight up smacked him upside the head and beat up on him as he held me into him and tried to calm me while I literally screamed "What if I did that to you?"
He didn't understand and having to remove myself from the situation before causing too much damage, I left.
All I could think was that if he couldn't go two flipping days without getting laid, he must honestly be in the relationship for sex and it was inevitable that he would cheat on me. And I put myself in his ex's position, envisioning myself living with him and I KNEW I couldn't put out every single day, I just wouldn't be able to. I'm not that kind of girl.
He texted me about 5 times as I was on my way home from his house and one of the texts said that he held her up to different standards than he held me up to, and then proceeded to say that it irritated him with her because they lived together. If he wanted to stay with me, that was a big no no.
He's made it clear that he's in this relationship for the long haul, and long haul to me means that one day, if we stay together, we'll have our own place. Having our own place to him would mean that I'd have to fuck him every single day if i wanted to ensure that he wouldn't cheat on me. That's what it says to me.

And It really sucks knowing that it's inevitable now that he's going to cheat, because I really did like him, and I even secretly wanted him to tell me he loved me and for me to say it back eventually. I mean, i actually wanted to get to that point. But now I feel stupid for even believing the best in him. Feel like it was all a dirty joke. The trust i'd built up for him has literally plummeted to almost nothing.
And I'm going to go have a talk with him tomorrow afternoon, but I'm of the strong opinion that it will end with me leaving his house single.