<human>: Give me the gist of the text in a nutshell

I've been with my boyfriend for about 8 months and things with him are mostly wonderful! We have a lot of (great) sex, and we're both very into trying new things together. I know he's had threesomes before, and it's something he's really interested in doing again.
Coincidentally, I also get off on the idea of introducing someone else into the bedroom, though I've never done it. 

I do have some reservations, and have told him such. I don't want this to ruin regular sex for him, I don't want it to be something we do every week or even every month. I certainly don't want him to have any contact whatsoever with the other person outside of the event in the bedroom. He knows all of this and is in agreement and assures me that in the past, it hasn't effected his sex life with his partner day to day. He also said the thought of watching me with someone else (female) is more appealing than actually doing anything himself (though I wouldn't make that a requirement).

He currently does not know how strongly I am considering the idea (it comes up once in a blue moon and yesterday he said he doesn't expect it to happen with me given some statements I made at the beginning of our relationship)... but the thing is, prior to that statement, I'd been considering setting up a threesome for him for his birthday (complete with Slave Leia costumes hahah).
My plan would be to find someone neither of us know, and they would have no means to contact each other after this. 

Now I'm just looking for anecdotal advice or thoughts from others who have tried it. So.... thoughts/opinions/stories...GO!
<bot>: 21f wants to surprise 23m with a threesome for his birthday (with Slave Leia costumes). Have set up some ground rules, now just looking for personal experiences and advice.