How long is too long to be in a relationship with someone? I think that 3 years is my limit. Is that wrong?

I would say if you are starting to feel that you'd even rather be single than be in a stale relationship, then I'd have a talk with your man and ask him if he has a plan to make you his happy wife or not.

If he says "things are cool the way they are, baby" but they are not cool with you, then tell him you want more. If he can't provide that for you, then you need to consider if you want to give it more time, or try it on your own.