When you chat to him express your worry at the whole situation, nobody should work like that, debts he can pay off, a divorce settlement is a lifetime of damage limitation. There is also the question of would the mood swings become violent, is he going to become a victim of domestic abuse? Maybe. His dad is not part of this either, if he's gay/bi or wants to be a tg/ts it's up to him and nobody has the right to judge him for that so anyone who does sadly isn't worth the time or effort.
It's going to be a long chat and hard to do but you need to be clear and concise as I've been there and if he's that comitted you will need to move a mountain to convince him otherwise. Certainly I've not listened when I should have at times so do your best to lay out your very real concerns for his wellbeing, happiness and future. If you keep it calm and clear he should listen and let him know you'll support any decision he makes and let him know it's not too late at all.
Good luck dude and get back to us if you need any other advice/opinions, friends like you are rare these days
