Of course, there are such reasons. If it is against your will, if you are not up to this act at that moment, then you can always say no. Your partner should understand and respect that. Or, maybe you are one of those people who feel neutral towards sex. They are called pansexuals if I'm not mistaken. Perhaps you just don't like having sex with other people and just don't like the thought of sex.
Nonetheless, there is always a way of satisfying yourself. For instance, various dildos and cocks. It is a way out for such people. I hope you are ok.
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