You can lose your partner a little every day, or all at once. Nobody ever gets to have a better partner than they're willing to give up. Willingly loving someone, knowingly setting yourself up for loss - that's hard for people. It goes beyond resolving sex problems or personal insecurities. It's an issue of integrity.
Relationships are a people-growing machine.
They pull and push you. They stretch you to the point where you can embrace the processes of life and love on their own terms. Like intense intimacy and eroticism, real love is not for kids. It's for adults only. We may not like the process, but it makes us capable of profound adult desire.