What Should I Do ? 😔

Me & my now ex Boyfriend has known eachother for 4 years now , we were Bestfriend's before that and was going out for almost a year , I don't know what to do ! I know I was the whole reason of us not being together no more because I am a complete Idiot , I let this boy stay around knowing that he liked me & me and my boyfriend was going through things so we were nearly separated at the moment as we work things out , well I let the boy that liked me to come over my house because I was bored and we had kissed , I regret it because it had hurt my Boyfriend so badly because I would go through our messages and he always would message me and I always ignored him and he would call my phone so many times it's ridiculous and I always ignored him , I was paying more attention to the other boy but , I didn't want to be with that boy I wanted to still work things out with my boyfriend , he is the only man I would see myself with , he is my baby , and now I felt like I lost him because I wasn't treating him right but I took that time away to change mentally so I can be a better girlfriend but now he is acting scared to trust me and I don't know why he himself said he knows I am loyal and good but I would never cheat on him again , I don't want to lose him ever , I see me and him starting a future together,