The relationship you have with yourself sets the standard for every other relationship in your life.
Not because it is a nice idea. Because it is the actual mechanism. The way you talk to yourself in private becomes the treatment you accept from others in public. The standards you hold for yourself become the baseline you allow in every room you enter. The love you give yourself determines how clearly you can see when you are not being loved well by someone else.
People who struggle to set boundaries almost always have the same root issue. They do not believe they deserve better. Not consciously. But at the level where decisions get made, at the level of identity, they have accepted a story about their own worth that makes tolerating poor treatment feel normal.
This is why working on the relationship with yourself is not selfish. It is foundational. Every other relationship you are in is downstream of that one. Fix the source and the downstream changes too.
Start by noticing how you speak to yourself when things go wrong. Would you speak that way to someone you love? If not, that is the work. Not the other person. Not the relationship. You. The standard begins there.
Russ Kyle