Sorry when I mentioned possible mental illness, I meant his ex wife not his DD.If I had to guess the answer to what happened is right here. The time for many mental disorders to rear their heads is right around the college age. It may be that your BF recognizes the changes in his daughter and is entirely unable and/or unwilling to accept what they signal. It would also explain his overly sensitive response to her being called a brat.
You say you're bothered at the idea of being excluded from college graduation, marriage, birth of a child, etc. IMO those are the least of your problems. You're looking at spending all sorts of holidays and events on the outside, looking in. I'd take a long, hard look at whether or not ever decreasing scraps is going to be enough of a relationship as the years go on, because that's precisely the future you need to prepare yourself for unless and until your BF is willing to address some type of peaceful compromise. If he won't discuss the matter at all, what makes you think things will ever improve? Are you prepared for the future to be nothing more than the current state of affairs?
No, I am not wanting the current state of affairs to continue, so I reached out for some suggestions & DISers have really delivered. I'm not the type that would simply sit & wallow if my DBF was spending time apart from me with his side of the family, that is to be expected. What gets me upset is the exclusion, not being asked at all because DD will be a part of the scene. So not okay with that.