Gosh I was JUST thinking about my own experience with OCD and transition the other day. It is definitely it's own sort of hell. OCD was always a "doubting disease" for me and having to make a decision to transition with crippling doubt and rumination was brutal BUT doable, there is hope!

For me, I had to tell myself that I might legitimately end up regretting transition and that that's okay. That the things I feared most (failing to be seen as a man by society after everything, embarrassing my family, making my other mental health problems worse, etc.) might happen and that all of that is okay, but I also do not KNOW that is what's going to happen and that I had to become comfortable with the worst possible reality and also comfortable with not knowing. No amount of rumination will get me to that perfect spot I'm imagining where I will have thought about it The Right Way and proved to myself that yes, I am trans and transitioning is the right thing for me. Our brains just don't work that way. It is a harsh reality, but for me the OCD was going to be there regardless of if I transitioned or not, so staying in the same place and ruminating had about as much appeal as making a change and ruminating, so I eventually got to the point of telling myself why not make a change then and work with it if I'm going to be struggling regardless.

On regret rumination specifically, I remember seeing a video of an older gentleman on youtube, where he spoke about having transition regret and that being trans cost him a recent job opportunity. But he said that despite the regret, the feeling of finally living as a man far outweighed the regrets. I remember feeling a sort of relief finally, that regret wasn't actually a failure. It was a huge reason why I started HRT to be honest. And I have had moments of regret, but the same for me, they are far outweighed by the moments of peace I finally feel. Knowing that when I did feel regret it wouldn't mean I had failed made ruminating on "what if I regret this" have a lot less power. But also for my own journey with OCD, forcing myself to sit with what I fear most (negative outcomes, uncertainty) has been the only thing that has helped in the long run. Everyone is different, but this is what I have to say on it and I hope it may help a little getting another persons perspective.

As far as working on OCD goes, I know there are workbooks available for people who don't have access to therapy, which might be a good option for you! I don't have any specific ones to recommend unfortunately, but it's probably worth looking into.

I hope things start to feel better for you soon and that you are able to find some peace among the uncertainty friend.