Friends with benefits' jealous ex girlfriend is getting in the way. Should I still get involved with him?

Anonymous
Hi guys so I recently entered a friends with benefits relationship with one of my 'exes' (we were friends with benefits before)

He and his ex broke up last summer because he wanted to see other people, but they are still seeing each other casually on a frequent basis. (I maybe get to see him once every 2-3 weeks even though Id rather it be a weekly thing, and he is seeing her twice a week). The sex is fantastic! (not just on my end, I make him finish fast which he loves ;) )
Anyways, he told me that she doesn't like the idea of me, and gets mad everytime he brings me up. She is very clingy, and he says that she needs 'more of a connection'.

A) Is it wrong for me to be jealous of how often they hang out. (I dont want a relationship with him, just a friends with benefits one)
B) Should I even get involved? Or should I mention this to him?
Friends with benefits' jealous ex girlfriend is getting in the way. Should I still get involved with him?
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