Ooo sounds painful, I've been there, the crying for days, in D/s relationship, being mono with a poly. Having to accept it because that's what my Dominant wants. Heartbroken and furious that he would be so selfish. I take a serious look when a relationship starts to interfere with my ability to function.
But with lots of reading this forum, journaling, therapy, meetings and talking with poly friends, I am able to reframe the above. I don't have to accept it, even if he is my Dominant, I always have the choice to leave. But I didn't want be released, so I explored the choice of changing my perception about the situation and my interpretation of what it means about him and about me. I learned that it doesn't really mean much about me, he still loves me. I learned that he is really really different than I am, that he can care for more than one. And recently he has demonstrated the emotional maturity, focus and self discipline to pursue the relationship without neglecting the rest of his life.
All that to say, it is possible to get more comfortable but in my opinion it won't be easy. Six years into my relationship I still don't know how this all will work out, but I've learned a lot about myself and him along the way!
About being on the surrender side of D/s: in many relationships transparency is important, he needs to know what you are experiencing. For me that was the hardest part. I wanted to be a good girl and I didn't want to spew all my emotions all over him. In an attempt to be good I just wasn't disclosing enough of what I was feeling. I took years to trust that he could handle it, it makes sense that you might need more than 7 months to learn what you can trust him with! And of course, I learned that it is possible to be sufficiently transparent without making a drama mess, just learning to find the time and the place to be honest, and honest more than I was comfortable. I wish you the best!
Me: mono, 52, serving S in a PE relationship for six years, living together since April 2012
S: has been poly since he can remember, 37
A: His new girl, under consideration