Love is no respecter of mere human laws, regulations and rules, it can takes us unaware and contrary to all human expectations. My hope is that he never cause you any hurt or regret 'cos You've taken one of the biggest and daring risk in this life and that is: RISKING YOUR BEST FRIENDSHIP FOR LOVE. This is not a mere sacrifice for both of you; expecially for him.
For the current issue: Ask her why she's ignoring you; it maybe a different reason. If it's about the boyfriend then your boyfriend has to prove and convince her(your other friend) in a friendly way that he truly doesn't love and may just end up making things worse with her.
In turn, he should stick closest to you to show the world that both of you are meant to be.
No one should make you feel guilty, you did ask her before making the decision and she let you. Tinaii_Fitrove