Non-monogamy (having more than one sXual partner) carries extra risk for STI/STDs. No matter what type of non-monogamy you practice, the more partners involved in your network, the more risk you have for catching something that could stick with you for the rest of your life.
For those who have multiple partners, there are also the considerations of others you are intimate with. Whether you are open with your other partners about being non-monogamous or not (or to what degree) is a seperate discussion on ethics. Here, the ethics center around our other partners being able to choose what risks they are exposed to, and being able to give truly informed consent to those risks.
STI/STDs are not just passed via intercourse, but also through things that used to be considered safer, like kissing. HSV-1 & 2 are both able to be passed through oral or genital contact, including open mouthed kissing. And we've all heard the somewhat infamous story about Michael Douglas coming down with throat/tongue cancer, likely from his love of cunnilingus, right??
As we are all finding out thanks to COVID-19, public health information is rarely complete, and continues to evolve as scientists learn more, and better studies get done. I know that some things have changed from when I first learned about STI/STDs, such as how herpes can be spread asymptomatically, and does not require a person to be having an active outbreak to spread it. Some people never know they have herpes because they never had an outbreak, and doctors usually don't test for it unless you specifically ask for it.
Why am I bringing this up? Because I think it's important to know what risks you are encountering if you decide to pursue any non-monogamous relationships. This foundation of knowledge can help to define the boundaries you need for yourself, mitigate the risks to yourself and your parnters, and communicate/navigate implimenting those needs in your relationships.
Because I am non-monogamous myself, these are practices I am more familiar with, and want people to know I am someone you can come to talk about these concerns with, openly and honestly. I may not always have all the answers, but I want to help you find the answers you need, and learn to practice what you need in order to feel safe in all of your encounters.
Want to learn more?
Safer Sex Guide by Whitman-Walker Health & Human Rights Campaign Foundation (may not be secure)