How can i stop an ex's disrespectful behavior with women and using our child to get 'some'?

k so my ex (and baby daddy) broke up shortly after our child was born due to his lack of letting go of his past (he kept in touch with all of his ex's and said how he wished they worked out and blah blah), i wasnt upset i was more pissed that he was playing so many people while he has a kid. well i tried talking with some of the girls but they didnt listen one kinda agreed that yeah if he is doing this stuff to me he would probly do the same to her. but other than that they let him play his game its like do females have no self respect these days?? well lately hes been asking for sexual favors and saying things like 'i watched a porn and the chick reminded me of you" its gross i try to keep things civil because we have a kid but just the other week he asked for a sexual favor with our toddler in the back seat ( i was in his car talking to him after he took our child for the afternoon) and i was like umm no well come to find out he was with or starting a relationship with a girl (i found out when i went on facebook and saw a relative of the girl saying he better treat her lil sis 'the gf' good tho she doesnt believe it will happen) and im disgusted!!! i have no ill will toward anyone i dont care what he does with his time but he brings our child to his place and hes seeing dada with a different chick every time(which is only time i noticed he really takes our child to 'show off' how he is "good" with kids but text me the hole time complaing he doesnt know what to do with him and has other ppl watch him while hes there, he also posts things about how he sees our kid when he absolutly did not one time i did text his phone saying 'oh really you took him to the park? then im baffled by what child i have with ME at the zoo' he then said that he didnt realize i took him to the zoo and planed on asking to take him out, he never did and he got comments from people saying 'oh how sweet' and stuff i just wanted to write on his post saying the exact thing i texted but i dont wanna start things publicly like that) i DONT want my son growing up thinking girls are objects and i also dont want these girls treated like this thinking they are in a decent relationship when the man is trying to get 'action' elsewhere. im not jealous i actually do wish him the best but this is just so disrespectful and i feel like i should do something but im not sure what i feel if i talk to the girl she will name call and say im just trying to get back with him (when im quite happy in the relationship im in) im not one to hang my dirty laundry on the internet or to start drama but i really wish this would stop any ideas how???