The ability to leave changes the quality of what you choose to stay for.

Staying is worth something different when leaving is genuinely available. If you cannot go, your presence tells you nothing about the relationship or the job, because it might be need rather than choice. Building the ability to leave is what makes staying meaningful, and it usually improves the thing you stay in.

Work on whatever would give you options, whether that is savings, skills, or other relationships. Not as an exit plan. As the thing that lets you know what you actually want.