Rabbi, can you please give me advice on a few things?
1. How can I focus better when I pray?
2. How do I move on from something I might not be able to get closure for? How does one get closure?
3. How can I not let the OCD get in the way of fulfilling mitzvahs and having my religion?
Looking inside the siddur while praying is very helpful tool to focus on what we are saying.
Regarding your other two questions, there is no generic answer to them, and there is a need to know the specifics of the situation in order to advise anything. Additionally, these issues may need a therapist to help you out with them.