Do you think that this male friend of mine is still boyfriend/partner material?

I think he's BSing you with his gf not being a long term commitment and won't work out. I think he does value and like his current gf and I think he's having some fun with you, cause he sees you allow it. He also seems the sort of guy who indeed doesn't take life seriously and he probably put his sense of humour into your comments about his gf cause - I suppose -, if he took them seriously, he would tell you to stop bad-mouthing her. And you should know, it's not the most attractive thing for a man, to see another woman bash his current gf or anyone else he's close to, for whatever reason. So to sum up, it seems he's just having some laughs and giggles with you, cause he sees you let him. If you stop letting him, he won't. Either way, I would stop it, cause -good or not- he is in a relationship and HE should decide when to end it. He didn't yet, which means he wants to be with her. And that just makes you a tramp, I'm sure you don't want to be that.