Maine is a tough place to grow an aloe to start! It is difficult to say what’s at the bottom of its declining condition but here’s some recommendations. I know its a very short season by you but take advantage of what you can. As long as your night temps stay above 45 degrees, move it outside into full sun. The leaves (when healthy) should be standing somewhat up, not flopping down. The center is also very pale and weak looking. These are all signs of not enough sun and maybe too much water while it was inside for the winter. Just to be on the safe side, cut off that leaf that is turning black – it could be a fungal or bacterial infection. Use a sharp knife and cut it off right next to the trunk and toss it. Sprinkle a good amount of ground cinnamon on the cut of the main plant. It is a natural anti-fungal, anti-bacterial. When you water, water well, but don’t water again until the soil has become dry to at least an inch or so into the pot. They need to dry out between watering. Just maybe it will start to perk up before you need to bring it back inside before your first frost.