How to get a Minecraft account back?

Ok my account wasn't really stolen but I need help to see if I can get it back. I've had my account and can still log in with my password and all so it's fine. But I gave my boyfriend my account so he didn't have to buy it himself and now we're broken up and I just don't feel comfortable with him being able to play it. He hasn't been rude about it and he didn't change my password or anything but i don't want him having that power. Is there anything I can do so that I can kick him off the account so he can't play anymore? I've already changed the password but can he still play? I just don't want him to be able to play it anymore and I'm not sure if there's a way to make him stop being allowed to play the game. Please please please help me if you have a solution! I would be so greatful!