He is cheating on his girlfriend with me!?

ok so its been going on for a month i met him in a club in town and was with him i thought that would be the end of that then he asked my friend for my num she gave it to him and he started texting me then people started saying to me that he had a gf and i didn't pay much attention really then he told me to add him on bebo and i did and i found out he has a gf i said it to him and he said not really they are not talking but then i realized he was with me when he was going out with her and still is. he asks me to meet every single day that's the truth i met him once when i wasn't even sure if i liked him and now i do like him and i know i shouldn't he texts me all the time and i say it to him that he shouldn't when he has a gf but he says that shes not really his gf but like i dont get it i met him last night again and i really really like him now. when i was with him last night his gf rang him and he answers right beside me saying he is at the gym lying to her and then he says bye i love ya and he says to me amnt i so good she believes it all. i feel bad but hes always telling me he likes me more now i feel sorry for the girl... what is your opinion of this situation