Ok so to be straight here your mom texted him? What did she say? I know I'm being really nosey but maybe its your mom and he's not returning the feelings. I know my mother acted like she had a major thing for my husband a few years back but he didn't recipricate. I had my doubts but he was very truly being honest. Drove a huge wedge between me and my mother though for a while. We moved like an hour away and Its better now. Maybe look at all angles. And if he is for sure cheating he probably isn't going to quit. Your just dating this Is just a preview. You don't want years of that. You deserve better.
By the way in case I forgot to mention it..... a boy cheating on a woman (yes I said boy because they do jot deserve to be classified as men) is not anyone's fault but his own. Do not let anyone make you think for one second you deserve it or that its your fault. All they're doing is trying to reroute their blame or guilt.