Been there, done that, got the T-shirt, and the heartbreak.

This is not a problem one person can solve alone. It takes two to realize there is a problem. The exercise comment is good. Exercize is good for depression and libido. Sweet talking is good. But most importantly is just paying attention to each other. Do things together that are very low stress so you can concentrate on each other and how you feel. Talk of your feelings and ask about the SO's feelings. Don't try to wheedle. Don't push. Give SO plenty of time to formulate thoughts and consider answers.

And rediscover romanticism. Eat by candlelight. Spend time with each other without the TV on. Read the Sunday paper all cuddled up together. Take a walk and hold hands. Play strip poker. Take a long drive with no real destination. Bathe together. Give each other back rubs. Basically just rediscover each other's bodies.

Good Luck!