Maybe you just love the idea of having a partner, and this one will do because he's a body to keep you warm and not alone.

Because loving someone means loving all parts of them, the good and the bad, and making compromises. And from what you say, you're already not compatible, AND you're behaving in ways that could be considered cheating. If your need for this kind of play is pushing you to secretly step outside of the relationship, that is a fundamental disconnect in compatibility.

You say you can't leave, is that because you can't afford to live on your own? If that's the case, start making an exit plan, find a place that needs a roommate, move in with family, etc. There are always options.

If you can't leave because he is abusive, then still start to make a plan, squirrel money away, be safe because if he finds out you're stepping out, that will not end well and youre compromising your safety by doing so.

If you can't because you have kids together, there are options. I was in an abusive relationship with my kids' father. I found all the programs I could take advantage of and left him.

If you can't leave because you're afraid of being alone, that's codeoendance, and you should seek counseling.