I'm betting its because of his subconscious, he's been thinking about the ocean forever and its probably the only place where he can get away hence why he's trying to kill himself unsubconsciously yk( i hope thats the righr word but either way its all in his head, unless im proven wrong next chapter)
I mean, he thought about being tired, wanted to rest a little, and all he has in his mind is his grandma. And grandma liked the ocean.
I meant it as he didn't want to drown himself there, this urge for the water came from other parts of his mind. Dying wasn't in his plans, but would have been okay with it, if it meant resting.
And I wanted to ask generally, why the water? Why is it better to die in the water?
Why the ocean? I know it was unconscious… but why that?