You should ask her but you should trust your girlfriend especially if she hasn't gave you any reasons to not trust her. i feel in any relationship you half to trust your partner you could try spending more time with her planning more things to do with your girlfriend so your mind is at ease about your girlfriend and trusting her plus if shes with you all the time it pretty much tells you right there shes not lying or cheating on you
Well you can usually tell by the tone in someone's voice or the look in their eyes or face that someone is lying. You can maybe straight out ask her but if u think she's lying she may also be lying about lying. Another suggestion might be to snatch her phone...
You can tell by her actions towards you and the way that she treats you. She will also want to be around you all the time and let you know where she is all the time. Knowing some of her closest friends will also make you feel secure.
You can't. Not for sure, unless you catch her in a lie. Once I catch somebody in a lie, I doubt everything else they say. I think if somebody will lie about one thing, they will lie about other things. But, don't make the mistake of accusing her of lying if you don't have proof. HUGE mistake.