Hi and welcome to PC. It is very friendly and supportive here. Forums and chat are good.
I hear you and totally understand about holding onto things. I do it too. I don't intentionally do it but I can't let go of my past, or trivial everyday events that happen to me I take really seriously and let them bother me more than they should.
It's just a matter of being self-aware, realising that this is what you do and work on changing this behaviour. One of the best techniques I have found is distraction or substitution. When I have intrusive thinking and am dwelling on something I find something to replace that thought. I just distract that line of thinking until it passes. logging onto chat and talking to others is a good distraction. Especially if someone needs help like in support chat, it is great to think about someone else rather than yourself. Hobbies, housework, physical activities etc are good methods to distract yourself. If you can't get past the intrusive thinking and it keeps going round and round in your mind, the best thing to do is write. Write about it. Either what you are thinking stream-of-consciousness like, or a poem etc. If I'm obsessing over an issue, event or person for example I will write a really detailed account of the thoughts and feelings inside my head. This is really good for re-reading at a later time, it can be very useful for getting to know yourself. It is also handy to give your T to read. This is good when you're in a quiet mood when you go to see your T. You just hand them your notebook and say "read this". That will get them off your back while you're feeling quiet plus it will give them valuable insight into what's going on inside yoiur head. They will also know that you are trying productive techniques to deal with your coping mechanisms. I keep a notebook for what I call homework. My T gives me topics to write about which I can choose to stick to or not.
It is great that you cut your friend off. You deserve better friends than that. For the maintenance and treatment of your mental health issues you need to surround yourself with only positive, uplifting people. Emotionally unhealthy/abusive etc people will only derail you. It is also great that you see a pdoc and that you are seeing a new T soon. It sounds like you are doing many positive things to aid in your recovery. Bravo. good luck, take care and pls keep us posted on your progress and any other developments.