Same here, Datun. When I first encountered a transwoman I felt nothing but sympathy. It was only when aggressive transactivists started doing things and making claims that harm women and children that I started to rethink. I explored a bit and came across the cotton ceiling. That was what made me hit peak trans - that moment when you can't go along with the agenda one step more.
Since then, the more I've discovered the more toxic the transactivists appear.
I suspect - hope - that It's the scandal of child transition that will first start a rethink. However, judging by another thread about transwomen competing against women in sports, there's already a pushback from coaches, athletes and fans. Everyone can see that men competing against women - and, inevitably, beating them - is unfair. Girls in countries which have scholarships linked to sporting excellence are being cheated out what may be their only chance at university. International women's events are being won by transwomen and people aren't just lying down. They're angry.
So there are various fronts on which people are starting to push back. The trouble is that, once the facts get out sport, about child transition, it's likely to erode the sympathy most well meaning people currently feel towards trans people, and people like OP's ex will suffer.
And once they're exposed to what the trans agenda really is, people aren't happy. We see it on MN often. Posters who have gone along with the idea that trans people are a sort of super gay hear some arguments, read some links, and suddenly understand why we're worried.
Our allies are facts, logic and the words and acts of transactivists.