- if they always face their phone down, then there is a possibility that they may be cheating. or if they have jumpy phone habits.
- if they act weird around you in public, they may think a friend of the other person may recognize them
- gushing or talking about someone suddenly
- friends acting strange
- if they act rude to you around other people (it could also mean they are just a jerk)
there isn't much i can say because you're only 10..