I can totally understand how you feel OP. Apart from anything else, and assuming that there is even £90k still in the pot when you finally inherit, that £90k will be worth a hell of a lot less, than if they were to give it to you today.
I do think it's terribly sad though when families fall out over money, so my advice would be, rather than not seeing or talking to them, to write them a letter expressing your feelings about the matter. Pointing out that you had to work hard to get your own home together, and think it only fair that your DB should do the same, rather than continuously benefitting from your parents generosity, which seems to only be toward him, and not to you equally, which is what a child expects from their parents. I would then suggest as a PP has, that if they have £90k to give away now, that they split it down the middle, and give you half each. That way you can go ahead and get any work done that you'd like on your own place, and your DB, still has a good start on a deposit for his own place.
You might also like to point out, if you do write the letter as I've suggested, that as they haven't yet made a Will, you are concerned that they might give this money to your DB tomorrow, but never get around to making the Will stating that you should get the first £90k, and that should the worst happen and they be killed tomorrow, having handed that money over to your DB, that no one would be the wiser as to their intentions regarding your share.
I hope you can get your parents to see how unfair they're being OP, but if they've always played favourites, then you might just have to walk away, if you feel strongly enough about it.