<human>: Throwaway, clearly. All names will be replaced with those of Scrubs characters, because.

I have been with my boyfriend, JD, for almost 4 years. On several occasions, he has expressed his interested in having a FMF threesome. I am not super interested in that, because I am pretty straight. That being said, I am interested in a MFM threesome, which he is not interested in. We figure that a good compromise would be to find a bisexual girl or a lesbian who is mostly into me.

As I mentioned before, I am pretty straight so it is not every day that I find a girl who I am attracted to, but recently, it happened! She is smart, sexy, super fit, blah blah blah... We'll call her Carla. The good news: She is a lesbian. We're friends, but not close friends, and we are not really in the same social circles. I have seen her maybe half a dozen times in the 9 months I've known her.

I recently learned that she is physically involved with one of my friends, who is in my social circle. We'll call him Turk. I know she told me she was gay, but apparently she is straight for him. I don't know what type of emotional relationship they have, but I have heard that she "doesn't do monogamy".

So my question is, do we go for it and ask her if she is interested? Do we ask Turk first to see if he'd be cool with it? Do we wait and see how her relationship with Turk progresses? Do we just forget about it altogether? 

I'm just worried, because this is the first girl, ever maybe, who I am pretty legitimately attracted to. I'm not sure when it would happen again, so I kind of feel like this is my only shot. But obviously I don't want to screw up Turk and Carla's relationship if they are in it for the long haul, or make things weird with Turk in my social circle. What's the most tactful way to do this?

Can you condense the text into a few key points?
<bot>: My boyfriend and I want to ask another girl to have a threesome with us. She is romantically involved with another one of my friends, but it is not monogamous. Do we ask her, or find someone else?