Struggling to cope

My boyfriend of three months, been together everyday for the last 10 months, just came out to me as trans and is wanting to move forward with hormones and having implants to complete their personal transition.

We live together, and we started off the relationship with a daddy dom/babygirl dynamic. I think that’s the biggest thing I’m struggling with, is that feels like what I “signed up for”. And it’s not like I’m not open to them being themselves because I’ve been nothing but supportive outwardly. It’s just inside I feel like I’ve had a rug ripped out from under me and I can’t comprehend losing someone I love to gain someone I don’t know. Maybe my thought process is off here but I want them to be happy I’m just struggling to wrap my head around it.