first, just simply ask her. there's a philosophy I once heard of about liars. when someone is asked a direct question, look at their eyes. if their eyes veer to the left, they are probably lying. if their eyes veer to the right, they are usually telling the truth. Anyway, if you still suspect after asking, look for the signs. ie: caring more about her appearance, work hours suddenly changing(getting home late), less interested in sexual relations with you, looking for reasons to leave(or not see you), may even initate an arguement with you as an excuse to leave.and finally what she wears when she's not with you. Hope this helps & GOOD LUCK!! MJ