Some details:
Me (M 26)
E (F 26)
B (F 33)
We are all queer identifying bisexual folk.
E and I are ling time friends from high school. Same dark sense of humor and impossibly cute. We reconnected 2 years ago, dated for a month while living in different cities (about a 2 hour drive) and ended when E wasn't feeling like a relationship was right for her. We remained close. We both did a lot of growing. 6 months pass by and I meet B online. Infectiously sweet smile, mature, headstrong lady. We shared a lot of good times but ultimately, she ended things after Thanksgiving dinner, saying that I just wasn't right for her. During my time with B, we attended E's 26th birthday where I had them meet the first time.

After B and I split, I made a choice to move back to my home town with family. I started spending more time with E again and we started dating a second time for about 4.5 months. Things again ended because E honestly didn't know how she felt about me. It upset her to admit that because she knew it wasn't fair to me to keep things going if that's how things were so we split again, again remaining close. 

A month goes by after E and I ended. E informs me that she and B have started a relationship. "Conflicting emotions" seems like an understatement, everyone.

I love both of these women and absolutely want the best for them because they are 2 of my favorite people in my life.
But... I can't help but feel grief here. It makes me angry at myself. I feel betrayed even though their relationship has nothing to do with me.
For now, I've maintained a relationship with them as friends separately but don't think I can comfortably spend time with them together. 
Can I ask for some outside insight?