Some thoughts on love that probably seem obvious to you wise folks:

The love we feel in the beginning of a relationship -- the excitement, the crush, the anticipation -- and which, I must add, we hope never goes away, is pretty selfish. The other person's presence gives us energy -- and doing things for them comes naturally, because you get way more energy out of the relationship than you're putting into it.

Later, though, the more selfless love comes into play. Giving to and doing things for someone you love even when you're not getting the MER, or Minimum Energy Requirement, out of their mere presence. Like you used to.

The marriage vows and covenants make us promise TO LOVE even when it's not easy. It's easy, for the most part, when you're dating. But after the honeymoon's over, and the dishes are dirty, and the baby woke up again, it's time To Love. To give energy, even if you're not receiving it.

I guess your energy supply gets replenished in a new way at that point -- maybe solar power.