I think, if David and Gillian really call their relationship « undefinable » it’s because they have such strong, deep love and are soul mates that go beyond any words and terms. I think that in our fandom when most (not you) people say they’re in an undefinable relationship it’s because they mean they’re fwb, or don’t really love each other, or fuck others, or are waiting for someone else. I hate that because it’s insulting to all that David and Gillian have accomplished in their relationship!

There are multiple ways to see Gillovny, and to define their relationship. They kinda all make sense, as long as we don’t have any confirmations. But, in my opinion, the fwb is the only one that doesn’t make any sense. Anymore, at least. It doesn’t work with who they are now, with the bond they have now. Thinking of them this way sounds like misinformations and biases. I also think RPF are somehow responsible for this headcanon, and I say that perfectly aware that I’ve written a bunch of nsfw ones! But some people tend to forget about the F in RPF, and forget that they’re still characters, and it’s not reality. We often picture them as two creatures made of lust, as two sex beasts and nothing else. Reality is something else! You just have to make a few research, watch videos, read articles, get to know them, and you’ll see that it’s not like that.

It could have been the case back then, and I’m sure that if it was, they wouldn’t risk to ruin the beautiful relationship they have now for a good fuck once in a while. 

I believe it’s the whole package or nothing at all, but I think something in between is just impossible at this state of their lives.