Dear Dmm15,
Yes, after four years you should know if you want to be with your partner. If you are still "always looking for something better" this means one of two things: you are with the wrong person or you have wounded places within yourself that create this type of behavior.  I would suggest that you really dive deeply within to discover

which answer fits you.  The great thing is that you already know your truth, it is just a matter of revealing it to yourself.  You can do this on your own or enlist the help of a professional. Either way, you are on the right track because you are asking and wanting to know.