I find it weird when people expect you to treat them better than they knowingly treat you. It’s the kind of strained relationship that will leave someone else feeling bitter. I think what is the best thing to come out of these kinds of interpersonal relationships is to let it fade or kill the friendship outright. Even if you never get to tell the person how you feel. It’s best to make those kinds of interpersonal relations die. There is no reason you have to allow yourself to be thrown under the bus repeatedly for someone who won’t leave the driveway for you.
There is never an easy way to bow out and let things be, some people need the closure, but I find that seeking closure are you allowing yourself to open old wounds again. Knowing your relationship, no matter if platonic, work, or romantic, is one-sided will only add to the imbalance that is already in place, so it’s best to move on quietly. After all, if you already know the person is selfish, what’s the point? The other person is aware, they just don’t care. Some people can care less how they treat you as long as they get to inflict the pain.
It’s up to you to care about yourself and be on alert for people who are only on your side when you cater to their level of respect for you. Well, I say, leave them alone, find people who really care about you and put all the power you would in salvaging a single interaction and learn to give that love and energy to yourself. At least you know self-love is reciprocated.