How bad does this sound?

I’m having issues with my fiancé. Contemplating leaving. I’ve never been a cheater but I don’t like the idea of leaving him before I meet someone else. I need a backup plan. Especially because I’m older and I want kids. How bad would it be to just drag things out with him and then leave him when I meet someone else? I won’t bore you with the dirty details and red flags I ignored ... but it’s been years and he’s put me through so many unforgivable things that I forgave him for. But I didn’t forget. And I resent him. I think we have irreconcilable differences and we just stay together because it’s easier than going out looking for someone else and starting over at our age. It’s not really cheating but it’s like keeping an eye out just in case something better comes along. I met a guy last week at a friends baseball game. I will see him at the next and final game of the season in 2 weeks. I want to see if I can get his number and flirt with him. If not then there’s no one else I can even think about hitting on or hitting up casually. I would have to wait to meet someone new and that’s hard these days. My fiancé neglects me and this guy is totally different and I’m intrigued. I know I’m gonna get hate for this. But I kinda feel like we’d be even after how bad he’s treated me. We do love each other but I don’t want to settle if there’s someone out there who would treat me better. Biggest fear is I dump fiancé never meet anyone never have kids or a family and I regret it and wonder what could have been with him. Maybe my temporary unhappiness with him will dissipate? Should I go for it with the baseball player? Thoughts?