Just because you have nothing to lose because you're single and only having fun doesn't mean you have to butt in to someone else's relationship and try to ruin other peoples happiness. Please respect a relationship.
Depends on the situation. Whatever I think of them I keep to myself because that's what decent people do. What I initially think isn't what I always think
I snapchat all of like 6 people everyday and that's sometimes just for the streak
Would you tell on a guy if you knew he was cheating?
Depends on the situation. If it was my best friend or someone I knew well and was comfortable talking to yes. I would. But if I hardly knew the girl I wouldn't. Maybe it's just me but I don't want strangers informing me of my personal life.