When you feel like you're missing something in your relationship I think it would not be uncommon to think about past loves. You'll only focus on the positive memories and dream about the days of that rush.
My advice would be to start doing little things again. Act like you did when you first started dating. Surprise her with something she loves. Take her on a real date. Text her randomly and tell her you are thinking about her. Ask her how her day is.
Have a night where the two of you both put away your phones and focus on each other. It sounds like she misses that dopamine that you get from a new relationship. That adrenaline that gets your heart pumping and the attention.
11 years is a long time. I agree with the marriage counseling. I am sure there are things you are both missing and a third party can help greatly.
Also...as a woman with kids (not to pry) but having that random intense sex where you take her by surprise and um... well really get her going. Make her feel beautiful and wanted... well that will send a surge of dopamine and Oxycontin. If you give her that to focus on then she won't feel the need to talk to someone else.
That's just me personally.