Failing quests really sucks. As much as I want to enjoy it, the combat is holding everything back, even on easy.
There are 9 endings and yes there's a gallery for after the first time you finish the game. The endings are not fully finished yet and aren't viewable in the gallery but they are tracked for future updates, so they'll become viewable for players who have collected them when that feature is added.
There are 4 endings for each companion and protagonist combination. After you go on 2 dates together the final quest will start, finish it before time runs out. Alternatively defeating the cauldron after getting all of the location clues is always available if you have missed your chance to get a companion ending.