Wow, that's a lot to tackle. I am definitely not the advice guru here on PC, but I see no one else has answered your post. I have a few random things I noticed that I can throw out there that may or may not be useful to you.

Your Brenda sounds a lot like my "Sally", my girlfriend from high school and my early college years that I was sure I was supposed to marry. It took years after our marriage that my wife finally stopped feeling threatened by her, or rather by what she felt was my idealized image of her, even after I eliminated all contact with Sally. The question: is your relationship with Angel important enough to cut off contact with Brenda for Angel's peace of mind and security?

At some point you probably need to figure out what happened when you "kind of" slept with Brenda. Seems like Angel is threatened by it, whatever actually happened.

Therapy might be a good idea for you to help you sort out your feelings and deal with this idealized woman you believe you are trying to see in both Angel and Brenda. I know what I'm talking about on this one; I have an idealized image of an ex lover that's causing lots of damage and preventing me from restoring my marriage. You need to get past this and realize you are in love with a human with all her faults and flaws. Difficult to do, I know, but not impossible.

Couples therapy might also be a good idea for you and Angel if she's willing to go. If she values your relationship she will go with you. If she won't go, that tells you something about where your relationship stands.

I am completely unqualified to address what Angel feels about you and Brenda and the whole relationship because of her spirituality. There is one person in particular here that would be very well qualified; I hope you get a response from him/her.

That's all I have for you, my friend. Sorry I didn't solve all the world's problems, but I hope I at least gave you a few ideas to think about. Good luck.