My bf (22 m) & I (20 f) have been together for 8 months and we love each other, but he used follow sexy girls on ig private & public pages... I confronted him, and I told him it makes me uncomfortable! I ask him why he does it and he never says the answer only that he stopped following. He did this 3 times until I told him that I wanted space. We talked and we still together but my trust for him is not the same. Did I overreact?
There's a lot going on here. Your question is "did I overreact," and I'd say that's a tricky question to answer on a lot of levels.
Did you overreact to him following sexy girls on instagram? From my perspective, sort of. It's not like he's doing anything besides looking at them. Just about everyone likes looking at sexy people, and that doesn't usually threaten their current relationships. Unless he's comparing them to you, pressuring you to lose weight and contour your butt or whatever sexy instagram ladies are doing these days, it's not super impactful to you.
That said, that's my perspective. You said that it makes you uncomfortable, and you have the right to feel your feelings. You could try to rationalize yourself out of that discomfort, but you're not obligated to, and you might not be able to. You did the right thing by letting your boyfriend know it made you uncomfortable, and clearly outlining what you wanted him to do.
It sounds like he wasn't willing to do what you asked - which is his right! - but he did the wrong thing by promising to stop, then not stopping. If he isn't willing to stop, he should say "I hear that it makes you uncomfortable, but it's not something I'm willing to quit, so we need to talk about whether that's a dealbreaker for this relationship and move forward based on what we figure out."
Instead, it sounds like he kept following them, but told you he didn't. That's dishonesty, and it's going to feel like a betrayal even if it's about a behavior that, itself, isn't super consequential. I don't think it's "overreacting" to be upset when your partner conceals something from you.
But you've chosen to stay with someone who you know is willing to continue doing something you've asked him not to, and is going to lie about it. You say your trust in him is not the same - why are you still dating him? You don't deserve to be dating someone you can't trust; that's a painful place to be in and not a compromise you have to make.
1.) Am I willing to stay in a relationship with someone who follows sexy instagram models? If not, leave the relationship. If yes, then you need to figure out what your next steps will be to manage these feelings, and address the discomfort. You have to take active steps; don't just passively keep doing something that makes you uncomfortable.
2.) Am I willing to stay in a relationship with someone who lied to me? If not, leave the relationship. If yes, then you need to figure out how to start repairing that trust. Again, you need to actively commit to this choice, not just passively stay in a relationship with this background radiation.
There's also the issue of you wanting him to tell you "why" he follows them, and him being unable to. Maybe he can't articulate why ("I like looking at pretty ladies" might just be the whole story), or maybe he doesn't feel like talking to you about it would be emotionally safe. Think about how you come to the conversation and what you two can do to make it easier and safer to be honest with each other.