Sorry to hear things have not worked out as hoped. Sounds like your girlfriend would have to have some kind of major epiphany about polyamory before you guys could get back together again.
It seems wise to me that you are moving ahead with your life and doing what is best for all three, really. You can't just hold the illusion of getting along together. Everyone has their limits. You recognized those, and honored them.
I wish you a much brighter future, and true love along the way.
Love means never having to say, "Put down that meat cleaver!"