You

The term you typically refers to the person reading the message. However, there are certain exceptions.

Skill description
When the term you occurs in skill descriptions, it is referring to the individual casting the skill. Thus, if player A has player B targeted when player B is casting a skill, and player A sees the description of the skill activation monitor the phrase ... you gain 100 health..., the skill is actually going to cause player B (the one casting the skill) to gain 100 health, not player A (the one reading the description).

"You" is considered an ally.