William Shakespeare said it best in his sonnet 116.
This is an excellent mantra for all kinds of relationships. Most of us fall in love with the idea we have about another. Inevitably, our idea of the other collides with the reality of the other. That's when we might say, "You've changed". "You're not the man/woman I married". And, it's all true. We change over time. Life's circumstances change us.
Love is the way we treat one another, not necessarily how we feel at the moment. We commit to loving - whether with a child, a parent, a friend or a partner even when we can't stand them. We are loving when we seek to understand another; when we agree to disagree. None of this is possible without commitment.
Commitment provides the security and unconditional love we need to grow ourselves and our relationships.