I’m gonna have to guess that you’re young from the language, but I guess this applies to any age:
When people fixate on “small” things like this, it... isn’t about the thing itself. Him unfollowing her won’t make you feel better, not for long. Even in your post you acknowledge what you want is attention directed at you and your social media posts by him, not for him to never follow anybody else on IG
“Doesn’t go out of his way to compliment me” is an (understandably) vague way to define it. Some people need to be called beautiful hourly, some just want a special date night once a week, whatever it is. From your post it sounds like you might be overly insecure and want more constant reassurance than most, but tbh I don’t know. Does he NEVER say anything nice? Is he judgy or mean in general and you’re hanging on to this insta thing as a way for him to prove he’s not an asshole? OR is he actually nice, and you need an unreasonable amount of reassurance? Only you know that, unfortunately. If I were you I’d do my best to attempt being objective, see where the imbalance lies. Not to point fingers, but to see what has to change. Does he need to get used to being more complimentary, being lovey-dovey more often if he wants to make this work, or do you need to calm down and learn to focus on positives?
Not liking your last post is a bit of an odd one. I get why it stings a bit, but I mean esp now insta doesn’t even load old posts unless clicked, he might’ve missed it. Could you tell him that? Then he can just go through your profile every now and again and ensure he clicks “like”. Silly maybe but sillier things are done for our partners!
In general, social media or general non-relationship-related control isn’t received favorably. If my spouse told me to unfollow someone (that I wasn’t being inappropriate with) I’d get upset or laugh. Same thing if they asked me to, I don’t know, not wear air Jordans. Like buddy, this ain’t about you, what’s going on? Even if I hadn’t cared about that person on IG, I’d still not want to be controlled like that. This is assuming no special attention is given to the IG person of course, I’m not saying let him cheat