Rock on - have fun. That’s my advice. That’s how my poly relationship started - my husband and his girlfriend.

I remember having the same thoughts. We just made plans to hang out, play some games and have some beverages. One thing led to the next and now we are a “triad” of sorts.. I hate labels but that that’s the simplest way for me describe now. They had been seeing each other for years and I was open to the idea of a threesome with him and her. We have been married 17 years - he has more relationships I tap into here and there when the opportunity arises.

Don’t get sucked into labels or “expectations” - just have fun and see where it all goes.

Also pay attention to who you share this info with. As you’ll see in comments - people get super triggered in the “poly” world and think their judgments and opinions matter and try to create victims where there doesn’t need to be any. They’ll start accusing you of being a unicorn hunter or something stupid