Just a bit of info....you probably already know it, but just thought I'd share anyway......
Generally the risk of contracting HIV between two women is very low. The risk of HIV being passed on through oral sex is low, but it is increased if a woman has cuts or sores in her mouth, or if the partner receiving oral sex has sores on her genitals or is having her period. Oral sex is safer if you use a 'dental dam' (a square of latex or cling film) to stop any vaginal fluid or menstrual blood getting into your mouth. A condom cut open and spread flat can also be used for this.
Sharing sex toys (for example vibrators) can be risky. Always clean them well and have one each. This is one area of sex where sharing is a bad idea!
Rough sex - any sexual activity that can lead to bleeding or cuts/breaks in the lining of vagina or anus is risky, including 'fisting' or certain S&M (sadomasochism) activities.
My favorite activities with woman are dancing, undressing each other, taking photos of each other, having photos taken of us together, playing in the Jacuzzi together, kissing (mouth and breasts) and masturbating each other with our hands (and a dab or two of the new and improved KY). As long as there are no physical signs of a herpes outbreak and no open cuts on your hands.....this is absolutely the safest sex you can have.....other than being tested- waiting 6 months without having sex with anyone else and then if everything is clear you can go for it and do anything you want!
I understand your caution about safe sex, but with your husband having sex with 3 other women and with them having sex with their husbands. Who knows if their husbands are having sex with other women or not? The sex with the woman that you really like is actually the safest sex you can have if you follow the guidelines above.
The key to life is in being fully engaged and peacefully detached simultaneously and authentically in each moment.