Something very similar happened to me; I lost my best friend when I got with my now ex-girlfriend. It was tough losing my best friend but he didn't want anything to do with me as long as I was with my ex and I eventually realized that if he doesn't want to be my friend then I don't want to be friends with him. Often times I felt really bad and anxious and just plain depressed that I no longer could hang out with my best friend, but the thing that helped me most of all was going out more often and meeting new friends. The first party with old friends and I immediately started to feel better, and by the third one I was almost completely over him.
You say your mutual friend has also been cut out of that so-called "friend"'s life as well? Well, why don't you two throw a Halloween party and invite round plenty of friends and believe me you'll feel better and soon forget all about her. Friends coming over would most likely take pictures for social media and it won't be long until she'd see said pictures and realize what she had missed out on.
The boyfriend sounds somewhat controlling to me. Is it really all your friend, or is it part him as well? Before any real efforts should be made it is important to know who to direct those efforts at, and which would be most effective given the gravitas of the situation.
Leave your ex-friend alone for now -- don't give her a reason to suspect that you're actually harassing her. Believe me, don't give her and her boyfriend anything that they can turn against you; just let them get on with it; she needs to see that she needs you, not that she can't get rid of you.
Keep going, Staceylou. Also, congratulations; you're my first Q&A :D
