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You have multiple psychological issues surrounding sex and it isn't fair to project your issues onto innocent people. You get your head sorted out in therapy and leave them be. Stop pressuring your husbands girlfriend to be part of your family life. She isn't interested in that. Back off.
Spend time with sex positive people and stop using examples of drug addicts to equate with the bad things that happen with sex. If I told you how many men I've had sex with, you would shudder. But I use condoms with partners who are not regulars and have monthly screens for STDs. Never had an STD. Not even BV.
So go to your husband and his girlfriend, tell them that you realise you have no business controlling what they do in their time together. You realise that you have a unreasonable and irrational view of sex and you're working on it but in The meantime, you'll leave them to have the relationship they want to without your influence. Ask that your husband uses condoms with other people and reassure his girlfriend that as long as you can be civil, you'll stop pressuring her to involve herself with your family.