The most important person in each of our lives is our self. Truly loving someone else means that we are sometimes willing to reset our priorities by putting their happiness ahead of our own. If this is done out of loving devotion, it makes us happy as well, but our pleasure is secondary to the joy of the beloved.
But love is tricky terrain. If what we give our loved one is offered as a sacrifice, then it is not a gift of devotion but an act of martyrdom. We do it to enhance our own image of ourselves, or in exchange for anticipated appreciation.
There is a parallel in helping a stranger. If we do so out of need to be nice, rather than as an act of compassion, we are confusing manners with morals. If it doesn’t come from the heart, the stranger may be grateful, but for us it will still feel like a sin of pride.
It’s easy to confuse being loving with acting out of duty or ego.