She Is Just Too Busy- When your girlfriend is too busy to pick up the phone when you call she maybe giving you a hint that you just aren't worth the time it takes to go and answer the phone.
Or if her cell phone is always off even on the weekends its a clear sign that she doesn't want you to bother her. If she always has plans that never include you and she forgets events that mean alot to you.
Acts Bored Around You- If you finally get some time with her and she starts to act bored around you then its about time you woke up and smelt the coffee that she is no longer excited to be around you.
Also if she tries to find other people to talk with and hardly speaks to you all night or day then its time to move on to a new relationship.
She Will Fight Constantly- If your girlfriend starts fighting with you more often than she used to its a clear sign that she isn't happy with you any more.
If she leaves the house after the fights then she may have someone else on the side somewhere or may be going to the clubs to try to hook up with someone new.