Desperate for advice

My bf and I have had some issues from the beginning. I fell for him too quickly, which made him feel pressured to feel.the same way about me. We would break up for short periods of time but always end up back together. Until about June when he told me he just didn't think he could love me back and we broke up for 2 months. During this time, I continued reaching out to him, telling him that I was hurt because I loved him, sending him songs, etc. He told me it was over, to find someone else, that he was going to do the same. I was extremely depressed and starting seeking attention from other guys online. I just didn't want to feel unloved and lonely anymore. I ended up starting to hang out with an old friend of mine and we went to a concert. I posted on social media about it and my (at the time ex) bf saw it. He said that it hurt to see me with someone else and that he realized he had made a made a mistake. He reached out and I jumped at the opportunity to meet up and talk but I was also afraid it was all too good to be true so I kept my friend on the backburner. When he asked me about my friend, I downplayed it completely. I lied to my bfs face about a lot of things that happened during that 2 month period and some even before that but during other breakup times. My justification in my head was that I was afraid to lose him so if I admitted these things I'd be giving him a reason to leave again. I was so desperate to cling to him that but still doubtful in my head that it took almost a month for me to come clean. Now he doesn't trust me at all. He's done his part in showing me that he was serious and had come back with good intentions but my crippling fear of abandonment took over. He keeps finding things that I've completely forgotten about, which makes me look like I'm still lying to him. Anytime I try to express to him that I wasn't being malicious, that I lied out of fear, he says it's just an excuse. He doesn't recognize that the fear isn't there for no reason. He used to leave and come back all the time. as serious and had come back with good intentions but my crippling fear of abandonment took over. He keeps finding things that I've completely forgotten about, which makes me look like I'm still lying to him. Anytime I try to express to him that I wasn't being malicious, that I lied out of fear, he says it's just an excuse. He doesn't recognize that the fear isn't there for no reason. He used to leave and come back all the time.

I don't know what to do at this point. He is the very best thing that has ever happened to me despite the troubles we've had and I keep messing everything up. I don't want to lose him. I'm at a point in my life where I need his love and support to help me get past a gambling addiction I have picked up during times of deep depression. I have no one else right now. I know I was wrong for what I did. But how can I prove to him that I'm being honest now and convince him that if he continues seeking out things in the past, it will get us no where. I just want to start over fresh, prove myself to him and allow us both to heal and be happy with each other. I'm desperate for advice.