I guess I'll have to admit ignorance, I'm unsure what you mean by Body Dysmorphic Disorder. Yes I know I've looked on Dr Google, however maybe you might like to explain it in general terms - I'm not asking you to talk about you (unless you wish) - just in general terms as I believe you could explain it well. No obligation, just if you felt like it.
Apart from that:-
I've been talking with you off and on for a long time now and have built up a picture of what you are like, not your body, you. Your intelligence, your tastes in clothes, in music and so on. I also know from what you have said, both in the past and now your mother plus the the person in your abusive relationship both were very disparaging about you and your body.
Sadly if this goes on long enough a person will start to take what they say on board as if it were true. Completely unjustified to believe them, but it happens a lot. I have no idea why.
I would imagine this has a lot to do with how you feel now. If I'm on the wrong track please set me straight.
This can take over more and more of a person's thoughts, a horrible time. I wish it was amenable to logic, so one could convince oneself or be told that the thoughts are wrong. Unfortunatly that does not seem to work. I would think it is because the feelings are emotion which takes little notice of logic, or simple reassurances.
Going to a psych sounds a good move, and I'm sure in the long term will have a lot of benefit, however in the short term when in a loop of unpleasant thoughts in the night it's not a lot of help. So asking him to concentrate on those moments as well as the long term would be very sensible.
In my own case I try exercise, moving to another place, talking with people, books, movies, music and more, all things I can enjoy and look forward too.
There is a problem, jolting the mind out of its one way track so you are open to take in the movie, exercise, or whatever you find helps.
For that I use Smiling Mind (apologies if I've mentioned it before) the free smartphone app
It takes a bit of practice, but has exercises for everyone, no matter their concentration or motivation, there's even one for me (who's mind tends to want to revert).
It breaks the chain of thought, and after I feel calmer and ready to switch to something else. For me well worth the effort.
I don't know if any of this is of help, I would like it if you came back and gave me your thoughts