It's so depressing and it ruins my day , I feel like its been written in the history and can't be forgotten. I keep thinking about it throughout the day that's why it gives me a tendency to stay silent and remain in one place.
And also, the girl who is about to be my girlfriend .. It's my first time having one. But whenever I remember that she had boyfriends before, I feel like her ex is way better than me and I'm just a leftover ..

I hate the past :( !! Can someone please help/advice me , how can I get over the past whenever I remember it ?? (sorry for the bad grammar)

I have this problem too, I'll remember something that I've done wrong and it bothers me. I deal with this problem by living to my best ability without regrets. I tell myself that I made those mistakes and I've learned from them, I'm a better person now, I can't change my past, nothing changes with regrets, you can't rewind time, regrets are pointless.
I tell myself these things and it helps. Just remember that you are you.
Also, those other boys aren't better than you, she's with you because you're better, you may not realize it but she's with you for a reason.
I wish you well :3

Thanks ! This help a lot , Thank you Neko-tama :)