What I have learned thus far :

If you are not flourishing and cannot flourish, if a relationship situation is not life-giving to you, it may not be healthy (i.e. what is 'best') for you. Because ultimately, what is best for you is not an ideal or some chiseled chest or hot guy or a certain quality or musical taste. It's your own person state of well-being; it is only the 'best' for you if it is making you better as a person, and the other person is becoming better as well.

Think about what makes up the substance of your relationship. If the substance is sustainable and firm enough of a foundation to build a future upon, keep contributing yourself to it. If the substance is teetering its balance enough to survive the next tiff while shopping in the grocery store but screams of a threat for break-up at the next moment the other person is 'too much' or 'too little' of 'this' or 'that', do not lend your time to making healthy something that is sick and does not want to become better.

Ask yourself: what do I value?
After, ask: what do I realize I also value since being with this person?