Ah well, you see, the more experienced people generally understand that the vast majority of sexually active people have or will have herpes and/or genital want viruses so they tend not to be as bothered about sleeping with someone with herpes with precautions such as contraception. We have people on this board who have herpes and sleep with more than one person without a condom and those people also test negative. Anyway, it's up to you if you want to discriminate against people with a relatively harmful virus most of us will end up with. Many people do.
Back to your husband and his partner selection. Set boundaries where you do not share the same space or hear about his other toxic relationships and leave it to him. If he absolutely cannot manage to stop his relationships negatively affecting each other because he chooses toxic partners, that is something you might want to take up with him.
If I was poly and married, felt splitting absolutely wasn't an option but my husband continued to let my toxic metamours affect us, or he couldn't stick to agreements about how we prevent harm to our relationship, the only viable option would be to close the relationship. If I feel the only way to stop it was to actively manage his other relationships by imposing restrictions and setting the pace, I would opt for closing the relationship to work on us.