This was so beautifully written. Absolutely agree. Sex and lust in a long term relationship comes from:

1. Wanting someone, which is built in a long term relationship by taking the time to appreciate their beauty and wondrousness, and making time for it even in a busy day

2. Feeling wanted, which happens when your lover shows you in those million little ways, that you are seen, you are beautiful, you are desired.

And by focusing on the moment, on intimacy, on each other, that allows for times when perhaps depression, medical issues, stress etc mean that libido is low, but you are still keeping each other feeling wanted and wanting.