For the longest time, Apollo considered himself to be a strong person. However, it was always a little bit more complicated than that.
Though, that wasn't something he was really aware of.
Apollo knew it was undeniable that there were certain things in his life that were difficult to overcome. Things that could've easily broken him down entirely, but didn't. He knew that his heart and soul had become something different with time.
After all, diamonds were only forged under high pressure.
But in the end, Apollo wasn't invulnerable. Just becoming strong doesn't change the fact that one could get hurt. That the scars left over were still painful to bear.
And so, he tried to keep those bad feelings buried as deep as possible. Instead of dealing with those problems, he forgot about them.
It was just far easier to do so.