Is a a good idea at this point, or will it further complicate things?

My boyfriend and I (we are gay) have been together for 3 years. I love him very much, but I have done some things that I am not proud of. One of those things included engaging in text/ with someone who has been a friend of mine for a while. Let's call him Robbie. Robbie and I never met (he lives 3 hours away). Long story short, my b/f found out and we had a little blow up about it. I apologized and swore it will never happen again (which it hasn't) and Robbie apologized also. He and Robbie became cool with each other sometime before this even happened, and I was certain that they would not speak again, but they have developed a friendship. They are REALLY close, but it does not bother me (I check up on their conversations just to make sure there is no foul play or hidden attractions. Nothing at all. Just friends). We have all since forgotten about it and moved on... I thought. Robbie told me yesterday that he likes my b/f and I. He does not want to have a RELATIONSHIP with us, but he wants to have with both of us at the same time. The thing about Robbie is that he is very ual, and for him does not have to be tied to his emotions. Its just . I am certain that he could walk away from the experience with no emotional attachment at all. I am pretty sure I could also, but my b/f is the person I am worried about. Robbie told me that he brought to idea up to my b/f a few weeks back and my b/f said he thought it would be fun. This is odd considering that I know how jealous he can be. I wasn't sure if that was his actual response, and I was curious to see if that is how he felt, so I told Robbie to bring it up to him again just to see what his reaction would be. I know I probably should have asked him myself, but I really did not want to start him to thinking that I wanted to have with Robbie. I figured it would be ok for Robbie to ask again considering the fact that they have already talked about it. I found out that his response after Robbie asked him if he would talk to me about it was, "Nah, if he wants to do it then he can ask me himself lol". I love my b/f and I know that does not equate love for me, so whatever happens in bed with the 3 of us would not change how I felt about him. I'm just not sure if my b/f is actually for it, or if he is only going along with it because he thinks I want it. Could this be the openness that my relationship needs or a disaster waiting to happen? Will Robbie end up being the 3rd person in our relationship? Could this work out? There are a million questions going through my head right now.