Well you asked for honesty so I'm going to try to give you that.

Full disclosure, I am a lesbian, I am probably younger than you (in my 20s), have never been with a man and I am not a parent. Also, I think men like your SO is incredibly pathetic. I say this to acknowledge my biases and ignorance.

You say your SO is "a great dad". My previous experiences with bihet mothers is that the bar for "a great dad" is incredibly low. It takes almost nothing for a man to be considered "a great dad". I think you need to take a long, objective look at who he is and what he's bringing to the table. How much childcare duties does he take on? How much household chores does he do? Think about these things and remember them. I ask this because transgenderism is not only inherently rooted in sexism, it is rooted in ignorance. It is a collective of men who have some of the most ignorant and ridiculous idea of what it means to be a woman getting together to roleplay. It is quite literally the opposite of progress and "woke", and if he has no idea what it means to be a woman, then he likely has no idea how much work you take on. He wants to experiment with gender roles- does that include doing the majority of domestic and childcare duties? Does he take on the brunt of emotional labor the way women do in a lot of relationships?

I don't want to attribute bad intentions because I don't know him, and I have zero experience with heterosexual relationships, but it seems like a lot of men are incredibly self-centered and cannot handle not being the center of attention when their SOs get pregnant or have a new baby. In a lot of these cases, men resort to abusive behaviors, or in the case of male trans people, transitioning and seeking attention elsewhere. There are also more nefarious interpretations like men "trapping" women in relationships by getting them pregnant before showing their true colors, but I won't go into that. I just think it's incredibly selfish and irresponsible of him to do all of this when he is a father and should be putting the needs of his children first. If he cannot handle this, he has had years to get out of your relationship or put off having children to figure himself out. He also went behind your back to take hormones from the sound of it, which I think is selfish and dishonest.

I understand that relationships are about unconditional love and dedication. And maybe it's because I am a lesbian and I have no love for men, but at the end of the day, there's a balance sheet; and on average, in hetero relationships, men are takers and women are givers. Studies have shown that (hetero) marriages allow men to accumulate more wealth and maintain better health- men who have been married do better than men who haven't. Marriage has the opposite effect on women- women who have been married live shorter, poorer, more miserable lives than women who have never married. Women take on more unpaid domestic labor even when both partners have equal earning. Women are less likely to leave a terminally ill spouse. Heterosexual marriages was, for a long time, a model of male ownership of women and the only model of hetero relationships. Even though we technically don't do that anymore in most parts of the world, it's easy for to fall into old patterns. I say all of this because I see a lot of bihet women getting milked dry by the men in their relationships. I think you should take an objective look at your relationship and decide what you're getting out of it and whether it's worth staying in.