See this is why you need to (at the risk of sounding insensitive) get out more.
You have a lousy self esteem as displayed by giving into a sexual advance you really didn't want.
You have a rather immature attitude to the sexuality of others. Your mother and your former friend are no more whores than you are.
People do odd things when fragility and intimacy share the same tent. Parents and friends are people who make mistakes and evolve in ways we may not expect. You are a person too and you should be prepared to learn positively from your errors, It's not nice, you may have regrets and from time to time wonder what life would be like events had played out differently but to dwell on these issues is very unhealthy.
I recommend a dose of ritual activity. Along with the usual domestic tasks of cleaning your own clothes, tidying your own living space and preparing your own food you should set some time in the week to mingle. Walk somewhere, talk to strangers and maybe join some sort in some sort of activity where have to interact with real people who aren't on the end of a computer (even and indeed especially if at first it seems a chore and maybe even uncomfortable).
This will remind yourself that the sort of uneasy weirdness you feel is actually normality. And stable, conventionally uneventful happy lives are 90% myth. Most of the people you will meet after some investigation will prove to be at least as screwed up or as stupid as yourself if not more so.
From then on when life throws you something sordid you will learn to shrug it off after a few gripes.
For very good reasons modernity reminds us (and by us I mean mostly men) that no means no. So don't undermine that most important of mantras by ever saying yes when you mean no again.
Your consent to anything is one of the few genuine properties you own. It is the freedom explicit in your conscious awareness and if you throw it away for convenience sake you devalue everything you and everyone around you are.
Someone once said no to me once. It was horribly painful, terribly disappointing and the most defining moment of my life which I would not ever reverse. I was honestly rejected and I prize that more highly than fake acceptance.