Assuming both you and your partner 'read' as male the world will presume you're a gay couple. That's not necessarily true, you'd become a same-sex couple and 'gay' is more a way of describing an individual's sexual orientation. Whether or not that's yours too is for you to decide.

It's easy to say you shouldn't care about how people see and/or label you but we live in a society and people judge and draw conclusions. We are all sensitive to this to at least some extent. There's no shame in that and I hope your partner can also understand that while they become their true self this also changes your relationship and the way you see yourself. I hope you can talk about this together in honesty and with love.

If you find you're struggling I would highly recommend you speak to a therapist who knows their stuff or find a support group. You're not the first one to walk this path and it may prove valuable to connect with others who understand this first hand.

Your partner deserves all the love and support but so do you.

As a side note, I am wholly assuming good intentions here so no worries but using 'biological' is not typically seen as a positive phrasing in this context. I would use 'assigned female at birth' (AFAB) or 'identified previously as female', though I would also check with my partner as they may have their own lingo.