Do ppl cheat in unhappy marriages?

Both my husband and i are not happy with our marriage. Hes only staying for the kids, while im staying until im stable, and able to support the kids and myself, then im going to up and leave. He wants more kids with me, and he still wants to stay w me, even though hes not happy. But idk. I feel like hes already cheating on me, i just dont know. The majority of signs are there. And he did cheated on his ex wife for her friend, because he was unhappy, and they were having fights a lot. Just like we both are right now. I feel like what makes me think he wont do the same to me? Yeah, im stupid for still staying w him when i knew this. Also, in one argument we had, he said he doesnt like how i separated from him, asking me how i will feel like if hes going to cheat on me by having a side chick. So if i leave, he wont feel lonely, or sad, or want me back, because he already have her. I ask him if its true, and he said he was only using that as an excuse. Not only this, hes been telling me hes going to cheat on me in most of the arguments weve had. When it has nothing to do w cheating. He said i need to look at myself if he decides to cheat on me. I also hear that most ppl in unhappy marriages cheat. Is it true? Im not happy, but i wont cheat.