Should I stay with my boyfriend

Last year my partner was sexting with this girl on social media. He proudly told all his friends and family about it and I caught him and confronted him. His brother even encourages him to not be loyal. So whenever he talks to his brother I feel on edge. He didn’t meet up with this girl in person but he did message her about wanting her and this was crossing a boundary for me. I considered this cheating. We had a rough patch but decided to stay together. At the time when he cheated, he logged out of his accounts and changed his passwords. I feel as if to this day I still get triggered or something because whenever he changes a password or logs out of an account not I feel some type of way inside. I feel as if I need to quickly go search for someone I can have a relationship with incase something is happening again. (It hasn’t happened again except for that one time). I have a fear of being lonely so I’m not sure if that adds to it too. I keep wondering if this is healthy or normal in a relationship, to keep worrying every time something is changed or logged out. I try to stop caring but it gives me anxiety. It’s my first relationship and we’ve been together for 8 years and we’re both in our 20’s. I feel if we were to break up it would be too much for me emotionally at this point in my life. I don’t know if I could handle the emotional pain right now.