Leo was doing this as a way to save his friends.
Leo was doing this to save the world.
Leo was doing this so he could get back to Calypso.
Leo was doing this so his friends wouldn't have to.
Leo had been planning this long before he was a demigod.
That was the problem. He would sit there and tell himself that he was doing all of this so that he wouldn't really think about all those years, and all the thoughts running through is head. Sure, he was doing it to help his friends, to get back to Calypso, to save the world, but... What about all the other plans?
Right after his mother had passed away and he had jumped in that pool, he wasn't going for a swim, he was going to try and drown.
When he had run away for the first time and stood at the edge of a highway....
When he stood on the roof of the Wilderness School when Piper was in the room waiting on him...
When they had started out the trip to the Grand Canyon and it was going to be the final resting place for him...
After the quest was done he was already planning on it being the end so why not for a heroic reason?
But he couldn't leave Calypso there, he couldn't abandon her like everyone had done to him and really, he knew he didn't really love her he was infatuated but he couldn't be someone who abandons others... He just couldn't.
He tried to cover up all these thoughts, smother them down deep in the recesses of his mind, but really, they just came up in self-deprecation and being rude to people and maybe that was the point. They were meant to be rude. If they hated him, if they wanted him gone, if they didn't care, then he could leave. He could leave easier and not feel guilty for hurting them.