I don't know if it's worth telling my dad that I want to see a gender therapist. I asked him once before and he said he'd do anything that would make me happy, but then he changed his mind and told me he knows what's best for me and this isn't it. He's very liberal and for LGBT rights... just not when it's about me.
If your dad is liberal and pro LGBT+ then there is no reason for him not to support you. If you don’t mention it again he may just assume he made the right choice for you. Maybe if you sit your dad down and talk to him about how much it is affecting you and how seeing a gender therapist will help you he will have a change of heart. I hope things go well for you!