It must have already happened to you that your partner turned down your initiative for intercourse. Rejection in bed can be very unpleasant, especially if it keeps happening.
Do not bother yourself with the question why things are as they are, and check how you can face the challenge when your desire for sex is not as strong as it once was.
A threesome? Swinging? Anal sex? Spanking? A finger up the anus? You don't feel like trying this? How to say no to your partner's suggestions?