Dear Nicky8888
First of all, if you go out with a guy who cheats on his girlfriend, what makes you think that he won't cheat on you after you get in a relationship with him? he's obviously lying to his grilfriend about seeing you so there goes his first sign of dishonesty. he lies before and he's doing it now and he's gonna keep lying for his convinence. a guy will do anything to get what he wants from a girl. you're doing a good thing by denying yourself from having feelings for this man. don't ever feel hesitate to do the right thing. if i were you, i would avoid dating my co-workers. if anything happens, you'll be stuck with him at work whether you want to see him or not.
you're probably happy when you hang out with him because he's trying the best he can to manipulate you, especially older guys go for young innocent, naive girls because they can be easily manipulated. even if you get in a relationship with him, there's no future for you guys. you should be guilty knowing that you're with a cheating guy who has a girlfriend and two kids. i'm sure you can be a better person and do better than this. people make mistakes and regret later (especially girls), because they didn't know that they were making mistakes at the time. for you, you're only 17, but i can tell that you're a smart girl for noticing that you are making a mistake and seeking out for opinion. so do the right thing nicky8888. there isn't only one fish in the ocean. you have your whole life to live. make decisions with your head. i hope you make the right decision. goodluck.