My bf and one of his close friends have developed feels for each other. The friend is poly and knows that my bf and I identify as mono but flirted with him anyway. One night while they hung out and drank, they had a close call where they almost kissed. They now both realize that a sexual connection/tension has developed between them. My bf recently brought up trying poly, but I can't help but feel like he's using it as a fail safe and to not be accountable for cheating if it happens. Any advice?
The thing about polyamory is that it is not a “fail safe to not be accountable for cheating” - it’s a different way to think about relationships, feelings, and sex. If you two were polyamorous, and he kissed or had sex with this friend, it would not be cheating. He would still be accountable for his choices and their consequences, but “cheating” would not be the issue. Yes, it sounds like his newfound interest in polyamory is a desire to be with this other person without losing you - but you get to decide whether you are okay with that. Your boyfriend is essentially trying to keep things above board - letting you know that he wants to pursue a relationship with this person, but that he wants to do it with your knowledge and consent.
It sounds like you consider yourself monogamous and are not interested in dating someone who is romantically or sexually involved with someone else, and that you would consider it cheating regardless. In that case, you should not be polyamorous with this person (or anyone else). He can ask, and you can say no. He can then respond to that with his own choices. Polyamory is not a secret loophole where he can trick you into being okay with cheating; it’s a relationship framework that you can choose not to be part of.
If it’s important to your boyfriend to try polyamory, or to try a relationship with this person, he may choose to leave the relationship. You’ll give him information - that you only want a monogamous relationship - and he’ll have to act on that information. And he’ll give you information - that he wants to be in a relationship that allows him to be with other people - and you’ll have to act on that information.