What to do

Your story seems to have some missing pieces. Did they have a reason to bad mouth you? Did your ex not delete their comments? And what does he mean by they were trying to get him riled up? Do they have a history of harassing him about his girlfriends on FB? I don’t see his comment as gaslighing. I would have also thought he would have contacted you before 9 days if he really felt like you were hurt by the situation. But since you aren’t giving many details it’s hard to know if you overreacted to some silly comments or not. For example, let’s say every 3 to 4 months he’s “in a relationship” with some new girl. (I have friends on FB who are!) And his friends are saying things like “is this your latest victim?” “what happened to the last girl you were so in love with?” “is this one going to last more than 3 months?” or any variety of rude things guys say to each other.