Hey @Jake1,
Thank you so much for sharing all of this and being here. 
I think you ask a very important question. Letting go of things that happened in the past is something that many of us can struggle with. Whether it’s a difficult event, an argument, a mistake, a separation… we’re all meant to dwell on the past sometimes. But as you said, it can be out of control and really impact our capacity to focus on the present moment. Basically, to just live as we want. It feels like having a chain that keeps holding us to our past and it gets hard to move on.
People are right when they say that it’s a matter of letting go. But it doesn’t necessarily come naturally. It’s not a magic formula and it’s normal to wonder how someone can do that. I personally don’t have all the answers either. I too struggle with past experiences that were negative and keep impacting me in the present. But I found with time that welcoming those thoughts with compassion is a lot more helpful than fighting against them. I can’t always know how I’ll react in certain circumstances and I can’t be 100% in control of what I think or feel. But I can still acknowledge what’s going on, to take a break, name my emotions. It’s through that kind of moment that I’ll be more able to “move on”. Of course, it still comes in waves. But it’s like a circle that you learn to extend, progressively.
I guess my point is: try to give yourself some grace, friend. It is okay to be affected by things that happened before. It is okay to have a hard time to let go and move on. Some experiences require us to take our time to heal.
A thing that I find helpful is having a way to express those thoughts, whether it’s with your voice or through written words. When you let things out of your mind, you are taking an active step towards being free from those thoughts. If you want, and if you are comfortable with that, you are more than welcome to share those past experiences here. No pressure, though. It’s not an obligation, but a friendly invitation. Oftentimes, what makes us stuck with specific thoughts are the emotions attached to them. It’s those emotions that you’ll have to learn to deal with.
How those past experiences make you feel? And what could you do to ease those feelings in a healthy way? Whenever the thoughts happen, you can try to pause a little, name how you feel and choose something to do, like to close this chapter. For example, if it makes you feel sad, you can try to think about what you are grateful for. If it makes you feel afraid, you can try to say out loud that those experiences are not happening anymore and you are safe right now. If it makes you feel guilty, you can try to talk about it with someone you trust so they can help you find some clarity and you push away some kind of shame. What matters is that you do something meaningful for you. Sometimes, even just taking the time to say out loud “I decide to let go of…”, or to write it down as long as it’s needed, is enough. The more you’ll take conscious and healthy steps when those thoughts arise, the less they’re likely to burden you in the long run.