Wow. Sounds like a tough spot you're in.
My advice would be to dive right into the honesty pool and start swimming like crazy. If you truly love both of these women and you want a real committed relationship with both of them, you have to trust them both with all your secrets. Anything less is an insult, really.
I have found it amazing that my wife and I can be completely honest about what we want out of life after having discovered that hiding our true desires breeds nothing but longing and resentment. While poly is not the defining aspect of our relationship, it has been instrumental in our development over the last year. For us, being honest is more of a driving factor than protecting the other (or ourselves) from a difficult conversation.
Cliché as it may be, the truth will set you free.
Best of luck to you.
Concern yourself less with love and more with loving.