“so what about some1 in the same faction as you?
from reading the rules it sounds like he would still need to trust you. ”
It depends where you rank in the faction compared to them. Usually if you outrank someone, you're safe from them. Of course, they can also easily change faction and kill you under authority of their new faction. See the GNS for recent examples of this. It's hard to trust anyone, especially when a number of factions have been robbed blind by apparently "loyal" members, even leaders, with the appropriate privileges.
“under what conditions would a jedi/sith try to tell you if your force sensitive? ”
When they feel like it, basically. Some of them are friendly with certain factions. Some of them are paid. Some of them are just nice. But mostly your chances really aren't good.