Guys that are cheating on their girlfriend but act like their doing nothing wrong?

i've been friends with him for a while but yet he always wants to hang out, cuddle, etc. and he has a girlfriend.. and I know he's cheated on her because he's told me he's made out with other girls, yet whenever his girlfriend comes up in conversation he acts like he's doing nothing wrong. If I were his girlfriend I'd be beyond pissed at even the texts that he sends me.. I personally think he should be single because of obvious reasons. Are some guys just really like this no matter who their with or has he just not found the right girl yet? and I haven't done anything with him, because I would feel really bad if I did so don't bash me. just wondering why he's like this.