Feelings are, because they don't last forever. If only more recognized that fact. Lovely interpretation of it. The balloon in a good symbol to use since it's light and airy -like how feelings are, when you first have them- and then they eventually pop because it doesn't last. I'm thinking the black ink is what's left of those feelings, and it's usually drowning. I see the keyhole as where the heart is, and how feelings are said to come from there.
I kept thinking about this drawing and the cracked balloon and I imagine the spill to be liquid helium which would be very very cold and your description "Feelings are such fragile things" It made me feel sad