Well, the good thing is that that person is still in there. Your "old" self hasn't been replaced with this "new" persona. Your old fun, outgoing you is still in there, just covered up at the moment.
I understand how you're feeling all too well. I've been with my abf for 10 years. You have the option to not stick around so long and get back to living the life you want to live. Good luck, I know how hard it is.