I find it a bit odd that there is this "primary/secondary" struggle. She's hundreds of miles away and you've only spent time together 4 times in 2 years? Then you have 2 local partners (who happen to be married) that you see much more often?
You don't live with any of these people. Don't share finances, kids, a mortgage, a vehicle. I don't see a need for hierarchy at all. Obviously Lily is jealous that you see the others all the time, and even though she's far away, wants *some kind* of assurance she comes first in your heart, and sexually too.
Hm. Trouble that goes far beyond "safer sex." She's jealous, she's insecure in polyamory. She's struggling with your mono/poly relationship. It's like she's saying, "If you really love me, you will do this inconvenient annoying thing with your lovers of 10 years, that will remind you of me every time you go to have sex with them! Ha!"
Does your couple have sex with others besides you? If they do, --maybe I'd discuss using condoms, for your gf's sake, since she obviously doesn't trust the couple. But if you 3 are poly fi, then condoms are pointless.
I'd suggest, rather than going to condoms to satisfy her possessive feelings, she meet this couple, ASAP! She needs to view them as family, not competition. You've still got 2 more long years to wait until she moves nearer to you!
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
me: Mags, 59, living with:
miss pixi, 37