I'm not basing this on experience, just my thoughts so take everything with a grain of salt.
Have you sat down with yourself and thought about how you feel about both women? Why it feels right to love them both and share your sexual intimacy with them both?
When you are with one woman what are your thoughts? Do you compare them or just enjoy both of them for who they are on thier own?
The answers you come up with will probably apply for how your girlfriends will feel about you if they have another man in thier lives/beds.
Playing the Game of Life with Monopoly rules.
Monogamy might just be in my genes
Poly Events All Over