whilst i realise it's not entirely relevant, i'm very drawn to the original facts concerning your xh. i am assuming you were married during the 'cavalry officer' phase of his life and became accustomed to a rather different standard of living than you are now experiencing. were you working at all during that time? the difficulties of being an army spouse and entering the job market have been documented in a vast amount of research, but i would have thought that the 'soft' skills you picked up during that period in terms of organising, administration, event planning and hosting would have contributed enormously to your confidence and general employability, as well as bumping your determination to do something for yourself, rather than remain financially reliant upon someone else. but no mean feat to actually achieve that, and only confidence in your own abilities and sheer force of will could have got you out of that hole - with a small family you were potentially more reliant on his maintenance than when you were living under his roof.
so you have my sympathy, but ultimately i think you have to let the money/ xh thing go now. he no longer has to pay, and the fact he is continuing to do so is now an issue between you and your daughter, not between you and him.
i suspect the reason he is paying the money directly to his daughter is that he knows how tight money is in your home, and wants to be sure that the money he is paying to support his daughter and enable her to continue her education is actually getting to her, rather than being subsumed into the household budget and endangering her continued education. but this is speculation of the highest order, obviously.
i would let the next 6 weeks ride and send your daughter off to uni to become an adult. ask her for her keep, or give her the option for paying for her own stuff, but don't let it sour this last month or so before your dd flies the nest. it's pointless - and i doubt that the csa or your x are going to listen to your fury.
wishing your daughter the very best for her studies, and her first 'real life' experiences as an adult paying her own way. and i wish you and your new partner the very best in organising your future finances without the financial support of your xh.