"things were so good and easy before, but I just keep having doubts."
The point is, it was good BEFORE. Apparently it's not good now, and that's all that matters. Time to exit your relationship. You learn by doing--it won't be the end of the world if you exit. But it will be bad for you if you don't.
edit: you are having doubts NOW b/c it's the reality of the situation slapping you in the head, but you don't want to accept it for some reason. So it's not working out--time to move on. That's what dating is for: learning about compatibility. For some unknown reason, some people absolutely fear the ending of a relationship. Knowing that it's wrong is a blessing, but only if you end it.
Believe me, not ending a relationship that is wrong will lead to nothing but misery and anguish.
Additionally, not ending it when you should makes you extremely vulnerable to manipulation and control.