At times a relationship fails not because they both didn't loved each other enough. Rather one doesn't have enough love for himself/herself.
Inspite that, also no individual is entitled to be cheated or downgraded while in a relationship.
Perhaps, the entire scene is all about being able to give as much as possible without any sort of resentment, or feeling compromised. It should be selfless.
And all this is possible only, if you love yourself enough, don't cease your growth, nor stop living your life in order to give everything to the other.
Happiness is spread only when you are strong enough to handle your problems well, not necessarily only if your happy.