Try to avoid living together before marriage..
Too late.
In that case, remind yourself that the costs of moving your stuff out are trivial compared to the costs of continuing a poor relationship.
If you are looking for marriage, give yourself a deadline for deciding whether to get engaged or break it off. Share your deadline with a brutally honest friend. When the deadline comes, you and your friend can evaluate what you've learned about your relationship and whether it's worth continuing.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.