For those whom don't know Viktor Frankl, the man is a poster child for the best that mankind can offer. The man found ways to remain optimistic about humanity even through WWII concentration camps.
One of his messages is very powerful: If you do not expect others to be better or expect yourself to be better than you generally are, you will never give yourself the chance to become so.
In short: reach for the sky, you might hit the moon.
This is something you also see in relationships. Both partners attempt to be the best possible person for the other and perpetuate a lie of being better people than they are. Together, you shape eachother more and more into the person you want to be.
Do note, however, that this must come from a genuine wish to be a better person, not just from simple causal reasoning: If I do this and this, I'll get that back. The focus should simply be being there. To quote the deceased but not forgotten John Scatman : "I want to be a human being, not a human doing."
So how do you want to see humanity?