Leo Valdez's whole life was a lie.
It hadn't always been that way, at one point he was happy… well as happy as you can be with an MIA dad and flame powers. He had his mom and that was all he ever needed.
He would waste his days at his mom's machine shop. She helped him forget Tia Callida, his psychotic babysitter who tried to kill him multiple times.
With his mother he was happy, a now foreign feeling to him. His happy world crumpled the night of the machine shop fire.
He could never forget the feeling of hopelessness and desperation knowing that he was the reason his amazing mother, Esperanza died.
It was never fair to him, he always thought it should be the other way round. He died and she lived but the Fates were cruel and his mother's cord was cut far too soon.
He wondered why it was him. Why did Hera choose him? Why did Hera choose him? Why did Gaia taunt him until he snapped causing fire to roll off him like a furnace, rendering him unconscious and burning down the machine shop and his mother, already trapped, burnt to the ground with the building.
After Esperanza's death, Leo became quiet and withdrawn going from Foster home to Foster home, doing worse and worse things just to get away from the memories.
After a time he found that people like someone who can make them laugh. He became Leo the Prankster, Leo the Joker.
He pretended that he didn't take anything seriously and as a result no one took him seriously, but frankly he asked for it.
When Piper and Jason became his friends he was ecstatic, until they coupled up and left him as a third wheel.
He still had Percy, Annabeth, Frank and Hazel but they were couples and he wound up a seventh wheel which he thought was worse than a third wheel.
When they defeated the giants he was a fifteen minute hero before yet again 'The Fire Boy Freak'.
The other six had the glory and he was left to watch them live their lives without actually living his. He was on the outside observing without being noticed.