The guy at work

So lady's I have a boyfriend of 4 years. At first he was great. Then I got pregnant and he was a complete ass through the whole pregnancy and pretty much up until now (he started some antidepression stuff) he has just been a jerk. But we have been through a lot.

Anyways we got a new assistant manager at work. And you know how it is you keep your guard up until you know what kind of a person they are blah blah blah. Well I get along with him extremely well. He's super nice, likes a lot of the same things that I do. He's easy to open up to. We just get each other. But he also has a girlfriend. Now i would never ever cheat on the guy I'm with

But I just don't feel the same around him anymore and he has treated me like crap the last 2 years. It feels like there is a deeper connection with the guy from work though. And Idk if I want to bring that up because I don't want our friendship to get weird. But he does flirt. And I feel like if he were truly happy with the girl he is with now he wouldn't look twice at another girl. It's hard to sort this all out. Any advice?