I am old and jaded.
If you see the bubble over her head and it is not going into your PMs, she is whispering.
Does it mean she is cheating? No. But why can't she say it in public? Dunno
Maybe dudes are messaging her and she tells them go away.
In my experience, if you don't trust someone, there goes the relationship. No point in being bf/gf.
Bring up the whispers. nothing to stop her from going into message center and chatting that way. Or opening KIK while she is standing right there kissing you.
How is it going for you now?