A recluse.
Perfidious
Don't call someone
easy going
Someone who never goes to the deep end, cannot perform any type of stroke, and someone who never goes on the diving board.
Someone's age
Someone who goes back on or changes what they said, acting as if they never made the original statement, can be described as being disingenuous or hypocritical. This behavior might also be referred to as backtracking or flip-flopping. In more informal contexts, such a person might be called a "waffler" or "fence-sitter."
a diver
Text them, call them, or go to their house.
A free spirit
A tresspasser; the act of tresspasing
Call 9-1-1
You can call them. If they answer, the phone is on.