Why would he do stuff with me if he loves his girlfriend?

So I started talking to this one guy. And we automatically liked each other I guess you could say. We held hands like three or four times. And we kissed on the cheek like twice. And hes lied to girlfriend about where he is to be with me. But we have...

never done anything more than that cause he claims to loveee his girlfriend. Lol.
Umm what I dont get is why he would do stuff like with me if he loves his girlfriend.
Just recently we had this huge arguement where he told me that I had to respect his girlfriend or stop talking to him. And ofcourse im not gonna respect her, I mean come on right? And so I said no, and said please cause he still wanted to be my friend. But I was like if you want her then you cant have me. And then he said okayy, and I havent talked to him in about 5 days =/
What do I do?

you do nothing. if he has a girlfriend, you leave him alone, COMPLETELY!! if a guy is involved with someone, and is fooling around with you on the side, then what makes you think hes a decent guy to begin with. hes not worth it. he just wants someone to play around with. trust me, youre way better off if you just move on. there are other guys out there who would be much more loyal to you, and you would be happier in the end.

so I should just completely ignore him if he ever decides to apologize?