OP here. i think letting this build up until it explodes could be bad.
maybe i'll talk to my girlfriend about how i feel about her friend, and maybe next time me and the friend are alone i'll point blank tell her i want to have at least one sexual encounter with her (with my gf's consent of course) and ask her how she feels about the idea of being with me in that way.
ill be pretty casual about the whole thing, act like it's no big deal and make sure she knows it wont be weird after
