Wait, I'm a bit confused here. So, you're cyber stalking your ex and your baby daddy (for lack of a better term... or were you in a relationship with him at some point? ) who's a fitness guru who likes pictures of women who are super fit? Were you super fit when you were together or something? IME, guys who are into uber-fit women/bodybuilders are really specifically into those types. I think it's more a common hobby/obsession than anything... but that's here-nor-there.

And your ex (who I'm assuming is an ex for a reason) sounds pretty sketch like he might have been untrustworthy / looking to "trade up", and the personal trainer dad is into gymrat ladies which like I said... pretty normal. Why worry about what either is into today? I mean it's always tough when shared custody is a thing, but I'd say minimize interaction where you can. It's all about the kid and not the least bit about either of you at this point.

I'm a huge proponent of seeking out partners with a similar lifestyle so you can appreciate the same joys and struggles. Personally, I try (and generally succeed at) eating right and stay healthy and trim, but I'm far from being a ripped gym nut, so I tend to mesh with ladies who like me, are in somewhere the middle: Who like to stay active, but not to the detriment of other things in life. I have a few uber fit friends who spend A LOT of time on being active, and they've paired up accordingly.

As for the social media: IMO, just get off it. I quit everything besides LinkedIn and haven't looked back. It's just drama and time-wasting nonsense that could be spent doing better things.