Most Helpful Girl
I have the same situation except because I dated my ex for far less than 6 years. I think it's better to not disturbing him at the moment. Be friendly, but don't tell him to break up with her and get back together with you. If you can't do that, it means you better shouldn't contact him at all. If you love him you wouldn't destroy his chance to be happy, even if the so called happiness is without you. Just let him be. And when the time comes, hopefully you can find your own happiness.
I think this is for the best. Or at least this is what I am doing at the moment. :')