Am I overreacting or?

My boyfriend & I have been together for 4 years. I started dating him when I was 16 & he’s was 20. He is now 24 & I’m 20. The first 2 years of the relationship were complete shit. He was talking to other girls behind my back, he was commenting on other woman’s pictures and stuff like that. Last year in March, I found him talking to another girl saying that I wasn’t shit & that he wanted to speak to her. Within this time frame I also saw he would tell her he loved her & he would call her beautiful.. I was about to break up with him but I gave him one more chance. Ever since then he hasn’t been doing anything (not that I know of). Last night I found out that he was searching her up on social media & friend requesting her like nothing ever happened in the past. He says it was nothing & he simply just requested her. I asked him what business he has requesting who almost broke off the relationship & he says I take social media way too seriously.... am I wrong to get mad? Am I overreacting? He has never trusted me & I’ve never done anything in the relationship to say otherwise. I just don’t know what to do right now & I’m scared because part of me wants to stay but part of me wants to leave & break it off.