Never expect a man to do wrong to the mother of his kids... If you want a GOOD man, look for one who wants to be fair to her. On the other hand, if he lets her walk all over him AFTER the divorce is over & there is no more negotiating, the court has passed its' own independent judgment and decided what's right and what's wrong. THEn expect him to give her what the court says to give, and your biggest argument should be whether or not the extra that he gives is reasonable or if he's shortchanging himself or setting himself up for being exploited. (and that can be a BIG argument)... but realize that this is the big financial issue... they're his first family, she butters his first kids' bread, and you can't change that. If you wanted to change it, you shouldn't even try to. It's what makes him a GOOD man.
Whatever trust fund you have, you need to be productive. He already has one ex wife to support who is not necessarily being reasonable and earning her keep... what does he need with another who is always looking for someone else to live off of? Save your trust fund for retirement and find a job. And thank your lucky stars that you've found one of the good guys who is trying to do right by his estranged ex.
How a man treats his ex is going to be the way he treats you when he's angry at you... so treating her well is a good thing, not something to be angry or jealous about.