They are doing it, bc someone is ALLOWING them to do it. You have to put an end to it, no matter the cost. Whatever reason you're letting it go down like this, push that aside, and next time, do as you please - regardless. See what happens. IF, you adopting your OWN persona (fully) is a deal-breaker for your partner...well that's okay, bc that's a deal breaker for you as well. No one can be happy in a controlling relationship - you deserve to be loved for who you are, and above all, respected as an adult human being with rights and decision making power. Since you were 18 My Dear, no one has had the right to "tell you what to do".
Put an end to it...now. If it means the relationship is over....well at least you know NOW, not in 10 years when ur married with children...
PS - but on that note - lotsa a people just do it "bc they can". So leaving may not be the end result. If you "strap on a pair" and quit accepting this behavior, you may notice...it just goes away.