Why am i always thinking about a past bad experience... ?

you need someone to talk to, someone to care about.
we are not alone in this world. God send us here for a reason.
find a hobby like swimming or jogging, one positive exp will automatically replaces the old.
Talk to someone you know. I am sure there's still many good people in this world.
I was never for idle chatter, until I learned to open up to others and receive the blessings I needed from the community, and thus god.
Actually, you don't have to figure out why, only to find a way to comfort yourself and pray to lord often.
He will answers all your troubles, through your prayer. Let the past be the past. You are who you are now, right? So let's just get going. Find comfort through deep understanding and love, read interesting books.
The greatest obstacle is often found to be in ourselves. Trust in god's plan, we can overcome any difficulty we may yet facing. The past will be a valuable learning experience for growth and understanding of what's really going on, and most importantly, what really matters. Follow your heart, and through understanding you will find a way to harmonize your reality, and finally attain spiritual enlightenment. I hope this will help.

It's natural for the mind to wonder off to the past and worry about the future. Always remembering bad experiences is you're brains weird way of protecting you. If you remember the bad things it's likely you'll recognise them in present or future experiences so you can avoid them or move through them better then the last time. It's a survival thing. The fact that you're currently always thinking about them is likely meaning that there's something of similarity (the brain is also over sensitive so will relate the smallest **** as the same thing) currently going on or you have poor personality traits but guessing that you've asked this now I'm going to take a stab that you hadn't always done that. So it's likely you're brain to trying to tell you to be careful because things seem similar so it's reminding you of the previous life experiences of that. The biggest problem people can do when reminded of bad situations to current situation though they're in reality not the same is avoid it. Avoiding it will reward the subconscious response to that situation and it will just making it worse the next time you come across once again even the smallest similar thing. Just try to let it be. Don't wrap yourself in those thoughts or focus your attention to them but don't sit there trying to not think about it because trying to not think about something actually does the opposite and increases it. Just accept it, let it float on in the background of the mind and don't focus on it. When starting to try to not focus on thoughts you normally focus on, it can be hard but the more you attempt it the better you get at it. If you find yourself getting really wrapped up in it just think to yourself quiet calmly and positively "thankyou brain" it's a little technique that helps to lessen the seriousness of it. Still doesn't work trying focusing on your 5 sense one by one to bring you to the here and now and not in the past. Like what can you smell? what does it feel like to breath? What's parts of the body are touching what and how does that feel? What can you taste? What can you hear? What can you see? doing the 5 sense works by connecting you to your frontal lobe which is the more logical part of your brain whereas the back half which is the oldest is more primed for survival which is the part of your brain that makes you go back to the past.

Because you have not had counselling.

You are living in the past. Get over it and move on.