There is nothing wrong with either one of you. You just have different sex drives. I have had that experience with my ex-husband. Unforunately, if I refused, he would give me the silent treatment for days. There were many times I had sex with him when I just wished he would over fast.
With that said, counseling might help in the communication about the problem.
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Bipolar I, Depression, GAD Meds: Zoloft, Zyprexa, Ritalin
"Each morning we are born again. What we do today is what matters most." -Buddha