THE SIDE CHICK

I recently started talking to this guy, well we haven't even talk on that level. He is a costumer from my work and every time he comes we talk all the time. It so obvious there is a mutual attraction there. He's so funny, we get along real well. We have a lot in common. We have the same views in life but there's only one problem.. He has a girlfriend. Now I've met this girl before and she's real nice from what i can see but he just don't seem happy. Well we exchanged numbers and we started texting back and forth just friendly, flirty stuff. We had made plans to go out one Saturday and just get to know each other better no harm in that, we weren't doing anything wrong or betraying anyone so i thought. Well he cancelled on me because his girlfriend was home and couldn't get out. Even though i knew he had a girlfriend and i shouldn't trip off it it did bother me a lot so i texted him back and told him that i didn't wanna play with fire, that it was best to keep it strictly business and that i would see him around. He didn't respond and we left it at that. A couple of days later he texted me and gave me some explanation on what happen that night and why he couldn't text me back. I wanna believe him and by all means he might be telling me the truth but it doesn't change the fact that he still has a girlfriend. so basically i feel like I'm betraying myself because i don't wanna be "the other" i wanna be "the only". though i really like him A LOT and we connected right away and have this GREAT chemistry.i refuse to sell myself short and settle for less. its very confusing because i also think what if he's the right one? what if it grows into something bigger and better? but i cant let all the "what if" cover my eyes from the reality... HELP