why am I so insecure?

I feel like it's because, my boyfriend used to play a lot of games in the middle of our relationship. for instance, he used to download tinder and talk to other girls and he'd go long periods without talking to me. during which of those times I'd cry or medicate myself to feel numb. I've always felt that if you truly love someone, you'd fight for them... I never gave up.  He was my first everything, my best friend, my missing puzzle piece. During our breaks, I never pursued anyone else, he was always on my mind. I don't know why I'd stick around then but I was used to getting treated like crap all my life. I'm with him still and he's gotten better after that last incident where I had a mental breakdown on New Years; I told him all he does was hurt me, if he really loved me... he would never do this, I said I've stuck by your side through everything and all he did was "try" to replace me, am I not enough for you?, ect. I felt my heart shatter into pieces that night. I curled up and cried and he came and held onto me and told me," all that was BS, it meant nothing! you are the love of my life, all those other girls were just another text message and they mean nothing to me and never will! babe stop crying please, I love you" I know it's just a stupid app but it was the mere thought of it that killed. We both cried that night. Since then he's gotten so much better. I made an open phone policy where we both can go into eachothers phones, but I don't cause I respect privacy... he kindly agreed. he's become so much more caring and loving like in the beginning, we talk more. I love it, we've become so much closer... more than ever. Recently, he's admitted he played a lot of games and he knew it hurt me while he did it and he feels bad now. But lately he's been asking why I can't show how I truly feel... he calls it a "block"... I told him the reason why, which is all of what I said above. I still show my love in every way that I can, I kiss, tell him and show him all the time. he said there's no reason for a block because he's changed, he said he'll never do it again cause he's happy with me and I have no reason to worry or hold back... I am giving you my all. He proposed on the 30th and I said yes. Cause I can't imagine my life without him, we both are a little screwed up but doesn't mean we can't fix eachother for the best, I do want to show him my all, I have and I've done it before but how can I?