threesomes.

Okay, I'm feeling super awkward but oddly turned on. Okay my boyfriend and I have been together for almost 7 years, but for some reason girls turn me on. 
I have some girl crushes on instagram that are so hot I get all red just looking at them!  Anyways So now my boyfriend wants to find a girl to invite over to hang out and maybe hookup with. I've never been with anyone else, but I have made out with other girls before our relationship..  we made a tinder and it's him basically saying I have a hot girlfriend that likes girls... I have two questions, who has been in a long term relationship and has had a threesome?  And how you found the other girl?? Also, after you stopped having threesomes was sex boring?