i cannot process infidelity

When I was 18 years old, I was in a relationship with a guy I loved the most. He seemed more important to me than anything else in my life. And one day he told me that he was cheating on me and that fact tore me apart. I took 5months to process that. I tried to forgive him and continued our relationship but certain situations kept triggering me which I used to express and it led to arguments between us. Then one day he got tired of my complaints and dumped me. That has a traumatic impact on me and it still stays and now again after 3 years I'm in relationship with another guy. He seemed perfect at start. He made me feel secure but now that he's still in good terms with his ex and I feel her ex is a threat to our relationship. The same case is happening. My present boyfriend is tired of my complaints about my insecurity and problems and feels that I'm unable to give him peace. I'm scared if he might start getting peace from his ex. His ex will come to our college as our junior and their closeness will increase. Leading to an increase of my trauma.