How would a 3 person relationship work?

So here is another very long story (sorry). As many of my posts on this site entail, I have a boyfriend, and he is very caring and considerate. I've never had feelings for anyone else when I've been with him. Until now. Basically, this last weekend, I met this family friend of his who is 19. He is really cool. We drove around in my car for a while, got mcdonald's, went shopping, etc. Here is the wierd part. This guy was really cool and open, I mean; REALLY open. No filter at all really. I felt really comfortable being around him, and I think I even had a little crush on him even before the following thing happened. So, that next thing was pretty awkward. We were at the mall trying on clothes, and he was in one of the changing stalls, but I didn't know that. As the stall doors are always in a closed position, even when unlocked, I happened to push open the stall he was in. I guess he forgot to lock it or didn't lock it all the way, cause the door just flew open. Needless to say, I saw him in his underwear. Only here's the catch, what could've just been an awkward moment, tured into confusion. He was wearing pink female lingerie, or however you spell that. Also, where I would've been able to see a bulge of some sort, there was nothing. This dude had female genitalia down there. After about an hours worth of awkward silence, later at lunch I learned that he is transgender. Whether he is ftm without bottom surgery or mtf without top surgery I dont know, but he did confirm he is in fact female down there. He was cool about it, and after we were done hanging out, he gave me his phone number. Here is the issue: I've never felt attracted to another guy since I met my bf, let alone somone with female parts, now I have this huge crush on this guy I hardly know. What makes things worse, (or better, depending on how you see it) is my bf must have noticed the looks I was giving that guy when we were talking at lunch. You know, the "googoo eyes" you do when you have a crush on someone, and my bf said something! He then asked me if I've texted him yet, and I said no. He said "you know, kevin, if you want to do stuff with him, I'd be fine with it" this took me completely off guard. I've always been told that 3 way relationships never work out, let alone the whole cheating aspect of it all. My bf says it's not cheating if he says I can. He said really not to worry about it, and if it makes me happy, go for it. When I asked if he meant having him be "our" boyfriend, he said "if you want" and he sounds sincere! So if I go through with this plan does this work? Or will it ruin what me and my bf have together? I'm completely torn here guys. It would make me unmeasurably happy if I could be in an active relationship with both guys at the same time without neglecting either one, but if we didn't, I'd be indifferent about the situation as long as I still have him. I honestly don't know, this is the most complicated situation ever, and the transgender thing doesn't make it any better. My bf is gay, and he knows I identify as pan, therefore have attraction to this other person. How does this work?!? Agh! My brain hurts... please help guys, thanks for listening,
@Chip , or anyone else who can help.

 

I would want him to do what makes him happy, as long as it didn't affect our relationship in a negative way. He's told me that this trans guy, his name is Jon, is a pretty hot guy. So I know my bf is attracted to his looks aswell, I just can't imagine how he'd handle a sexual encounter with him. I think I'm going to go for it, or try at least, see how it works... I'll post updates

 

I don't know. I love my boyfriend and want to be with him forever. This new guy... well, he is hot, and my bf pretty much says we could do a 3 person relationship with him if I like. Whether it lasts or not is not known. Whatever happens, I just don't want to lose my bf.