The mediation is not going to get you any closer to getting him back. But you need to do this to protect your interests. Your H is probably in for a shock in regards to how much the D is going to cost him financially. Since you have been married for more than 10 years, you have a lot of spousal support (alimony) time (maybe half the time of marriage). Also, all the assets including retirement get split 50/50. You never mentioned if you had children.
The snooping is tough to not do, but you have to stop it for your own emotional sake.
I can tell you to not give up as anything can happen. In my case, I was pretty sure it was over and I filed a D. My W was cruel towards me, had our children observe her A with OM and continually threatend a D. Since that time, my W has given indications that she may desire to come back to our M. We have put our D on hold. I am fairly confident that she will come back, but if not, I am happy enough with myself to be able to move on (with a lot less money).
Make yourself happy in the meantime. If it ends in a D, you are much more prepared to move on in your life.
