You answered your own question, did not you? because your mother does not accept you for existing, you - to some extent - do not accept your own existence either. Part of existence for a human is a sense of personal space, personal boundaries, and an entitlement to privacy. When you acquire all of those, you will not worry about what others might think or say if they knew about your private life. Right now, due to the lack of definition of your personal space, your boundaries are non-existent and you feel that others' eyes might get through them and are afraid of what others will then think. So you need to deal with the legacy of having the mother you have and work on establishing yourself as a human, in her personal, private space and with a sense of boundaries and a (limited, of course) control over her destiny and choices. Sex is a fairly sensitive topic so that your fears flared up triggered by a sexual episode is not surprising, but it would be a mistake to focus solely on how to deal with the feelings triggered by the sexual encounter because you have a much, much bigger fish to fry. The issue is general and huge; the sexual encounter triggered a specific manifestation of the general issue, which is not sexual per se. Does it make sense?