And if she is looking at pictures of ex boy friends

I would not say it means she is cheating I would say it means she wants to see other people.

If she is looking at pictures of ex boyfriends,perhaps she is thinking that the grass is greener,if she wants out,give her,her out,and move on.

Don't wait in the wings,don't hang around,just vanish.

If she wants to talk about her reasons,listen to what she has to say,if it's a deal breaker for you,then you know,it's a dealbreaker for most people.