Dig deep to find the value in yourself. If you know your own personal value no one can take it away or negate it with negative treatment. It cannot be depleted when someone disrespects you, leaves you, or disappoints you. Once you own your personal value it resides within you and is a part of you.
Once you are of value to yourself you can then be of value to others. Personal value doesn't have to be comprised of monetary or superficial means but is rather something that can be manifested into a monetary gain at some point because of your deep belief that you are worthy. This makes it and you an invaluable commodity.
If the dynamics of a relationship change and you are unhappy with them, don't try to change the other person, try to change yourself and find value in yourself. When you rely on someone else to make you feel valuable you are setting yourself up for disappointment. You are only leasing your value instead of owning it. Find out what makes you unique, special individual, what you're good at and really own that shit!
If you are seeking to be valuable to someone else first, well, you are doing it wrong. Find out what gives you inner peace and value to yourself first and all else will follow. Others will see your value more clearly for what it is. Do not find your value in putting others down or comparing your live to others who are less fortunate, for that is only a facade of value.