My Girlfrined Still Loves Her Ex

My girlfriend, I'm in a relationship for over half a year now, has some down phases the last couple of weeks. All the time I want to help getting over her problem, she tells me that I cannot do anything because she doesn't know the problem and what is wrong with her. Maybe the hormones, she says. Then again, I know from a very close friend of ours that she says, that she somewhat still loves her ex, when she is in such a phase. That she misses him. She also says that she loves me and she doesn't want to give us up due to the lenght of our relationship plus she feels more safe and secure with me. So she says that she thinks that being in a relationship with me would be the better choice. But she doesn't know that our friend told me that.

Then again she still love him. And he knows that.

I'm kind of desperate now and don't know what to do. She always tells me, that she only loves me. And that this is the truth. It seems it is really confusing her.

So are her feeling for him due to hormones? Do I have to be frightened to lose her? I don't know what to do. I know I'm jealous. But that is because I love her so much.

I'm marked with a bit mistrust in women because in my last relationhip my girlfriend cheated on me. That is why I somewhat lost faith in love before I met my current girlfriend. But I still am frightened to lose her simply because she has feeling for her ex. The biggest problem for me is that she keeps this fact (her feeling for him) a secret regarding me.

I hope you can help me in this situation.