Story about people bonded to "Grateful Dead" type bears

Read this book quite a while ago in high school, 2004 at the latest. Details are a bit sketchy, any help would be appreciated.

Two people, one male, one female. I think that they meet up in the beginning of the story. The male is "bonded" to a creature who reminds me most strongly of the bears that are commonly associated with the Grateful Dead. He explains at one point to the woman that only men can be bonded to the bears, any women that have tried have…died? gone insane? Can’t remember. Part of the bond between them is that he gives the creature some of his blood every so often.

A majority of the story revolves around them finding and travelling through what sounds like an extraordinarily large warehouse left by a race that came before.

Near the end of the book the woman discovers that women can bond with the GD bears, but their bond is not centered around blood but something else (that I cannot remember).

It was a paperback book. I don’t remember there being any other stories in the book, so I don’t think analogy. There was either cover art or inside illustration (I don’t remember which) which showed something similar to the grateful dead like bears as the "bonded" creatures But the art may have also been little doodles at the header of the chapters, I can’t remember.

That’s it. Any ideas?

---

Here’s an example of the "Grateful Dead bears".