Welcome to our forum.
I would encourage you to try to have a positive outlook about this situation. Just because bad things have happened in the past, doesn't mean things will go badly now. There is extra love going around. That's a good thing. Love is a limitless resource. You are being honest with each other. That's paramount. You are thinking about opening up your relationship. That's the beginning of an exciting journey.
I highly recommend the book "Opening Up
," by Tristan Taormino. It covers a lot about polyamory and other forms of responsible non-monogamy.
Get the book and read it yourself, or perhaps consider asking your boyfriend to read it aloud with you. Ask him eventually to read it in any case. Talk about what's in there. Exchange thoughts and ideas.
If polyamory isn't what you want, you're under no obligation to practice it, and you're still welcome here no matter what. I just get the impression that having an open relationship is something you really, really want.
"This is all well known to my BF -- who has similarly grey conversations with his friends -- but somehow I feel like I'm doing something wrong."
Sounds like conditioned guilt to me. Don't let it rule over you. Follow your heart.