Here are some thoughts from a little bit of experience. That experience doesn't make them sacred, feel free to challenge them, add to or comment...
Lots of people in unfulfilling relationships seem unable to take a step back and ask hard questions about their relationship beliefs.
Instead they hear the same old statements repeated inside their head about what should be the case.
Some.. for reasons I may suggest later... are predisposed to associate a sense of shame to (only) themselves when these what-should-be's are not being met.
So those relationship beliefs… which you may possibly hold:
1) I believe that I am actually half of an… er… entity… e.g. I need to find my "other half", without whom I am incomplete.
2) I believe that I should not be more open about anything to anybody other than my partner.
3) I believe that a relationship should be for life.
4) I believe that a relationship can only end in hurt.
5) I believe that I cannot talk to my partner about the basis of our relationship.
If I can ony make one point in this post... these ideas are
beliefs. More later.