Why do men cheat in a relationship?

Obviously and a woman can cheat but I wanna know how men think about it (every girl's opinion is welcome of course)! So I have met a guy one year ago and we have been texting for quite some time when he told me he has a girlfriend and live together. He told me he likes me and the way we communicate. I like him too and I had started have strong feelings for him. I tried to keep distance from that, I was in a really bad mood. He stopped for a while and then appeared again and wants to talk about it. He told maybe he wouldn't break up. I told him again what he want from me he told the same, he likes me etc. Then he went travels with his girlfriend but when he was back he texted me. This girl has money, her job and her own home (where they live in). And once he told me they don't have sex (and maybe that's why we started talking but we don't do that too so I don't know lol). My question is why a guy who has his girlfriend and they seem in love on insta, they travel etc, cheat on her and then doesn't want to break up? and he tells me his feelings about me and he doesn't want just sex but he doesn't do anything for that. Sorry for the long post but I'm a mess rn
Why do men cheat in a relationship?
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