Seeking Advice: Introducing Threesomes into a Long-Term Relationship

I’d really love some advice on how to introduce the idea of having a threesome with my boyfriend. It’s nothing that my boyfriend and I have ever talked about, and I don’t know how to go about introducing the idea or where to begin.My boyfriend and I have been together for seven years, and we’ve been exclusive to each other through the course of our relationship. Recently, I’ve been thinking heavily about having a threesome to spice up our sex life. Ideally, I’d want a kind of friends-with-benefits situation: a guy who we both know and are comfortable around who we also can fool around with. Someone that we can play video games with and hang out with in addition to the sex. But at the moment, we have no one in our lives that fits that description. So, even on that front I don’t know where to begin.I know we’ll have to set boundaries and rules for this kind of thing, but I’m at a loss for where to begin. It’s not something I’ve ever dealt with before while in a relationship. I’d really appreciate any and all advice you guys can come up with.