I'm sorry you are going through all of this. You've been there for him, through thick and thin, and now to be cast away, instead of ounces of gratitude. Love can be blinding for many, and I hope, he wakes up and realizes the misunderstandings caused by a young girl in his life. I would, at least hope, that your boyfriend, would support you and try to find a way, to at least get you back into the important moments, such as race attendance and birthday parties.
Too bad, the four of you, couldn't sit down together, and just get this all straightened out. She may not be the ideal girlfriend, for him, but that's who he is choosing, right here, right now.