breaking up and back together 4 times

so my boyfriend has left me and come back 4 times now since 2018.
i have much love for him and I understand i had some issues such as my mental health etc and so did he but he always came back and i took him back because of that love.

It's just, I wonder, how could he ever leave me in the first place when i could never imagine it ever when we had issues? my instincts were to always solve them and get thru it rather than leaving. Why when he left did he follow loads of girls and explicitly show himself playing s*xual games and into women when they look nothing like me, and came back to me?

I do have insecurities and doubts and trust issues since he left so many times. since i saw all that^. It broke me everytime he left. Things are better now between us but not things like this, if i want to talk about it, he refuses to and it turns into arguments. So i have been keeping it to myself but its hurting me so much.

what are ur thoughts, i do need advice..