I've been with my wife for 10 years (married 2). I am a CIS male, and have suspected my partner (female sex, but agender) may be trans for a while now. They share a lot of similarities I've heard people who have come out have. Due to this, I played with the idea of if my partner was male, but confidently do not feel I'll be attracted to being with a guy. My suspicions have now evolved to the likelihood of talking to them about it after they sent me a text, right before their shift, asking if it'll be weird if they used he/him pronouns.
My partner is my best friend and can't imagine life without them. We've talked about our sexual orientation before and I've expressed to them that I am just not attracted to males. If my partner is trans, I'm worried I'll mishandle this. They have a history of depression (it's managed now to where they no longer need therapy and medication), and worry that my reluctance of being with a male may prevent them from coming out and worsen their mental health.
I am supportive of the trans-community, and resources on this subject I felt have not been relevant for a heterosexual male with a possible trans-partner. So how can I talk about this with my wife?