Should I stay friends or not?

I met a guy in February and we dated for a couple of months things didn't work out but we remained friends, every couple of months we meet up and have a couple of drinks, and one time we had sex with no strings attached, he also phoned up our friends before to wind our friends up then two days later he officially got involved with someone and has lied to our friends that we didn't have sex [I do understand why as we both have moved on] but his told me he wasn't with this girl when that happened anyway we remained friends but whenever I see him he keeps complaining about his girlfriend to me, saying that she's a nutcase and he can't end things with her even though he wants to, I advised him as a friend to sort it out and do whatever is best for him, yet every time I see him he keeps bringing this up every time we meet, he even text me once asking me to go to his without his girlfriend knowing, I said no of course, last time I saw him he told me he was on a eight week break from his girlfriend I just said that was up to him and to do whatever makes him happy and he invited me and my friends to his for a Halloween party after that he got really distant so I texted him asking him how he was, asked if he was still having a Halloween party, he replied saying he didn't know what was on my end of things? I haven't talked to him since, but I checked his girlfriends profile on fb and they are happy, why is he lying about his relationship to me? all this has left me paranoid and confused.

Dear Lilith, Firstly, in your relationship with this guy, who broke up with whom? Did both of you aggree to break up? From what I can see here, I think, one of you or even both of you have still feelings more than in a friendship. If this new GF is a "nutcase" why doesn't he break up with her? If he's lying about this I think he's ashamed of this girl in front of you and still has feelings for you. If something is really wrong with them you wouldn't see this on the GF's Facebook. Just think about it. Would you post pictures with your boyfriend with the smallest clue that there is a problem between the two of you? Of course not. You would post only pictures showing that you are happy. I think you should help your friend to break up with his "nutcase" if he's really unhappy. It's up to you whether you help him as a friend or as somebody who loves him. I think friendzone is always a bad thing. So try to avoid it. Good luck and keep me posted!