My ex is possibly more of a codie then I am and when we were seperated he opened my mail and I was sooooooo mad. Opening mail is a big crossing of boundaries issue for me.
To put a positive spin on things, use that information and move on in your recovery by letting go of what he is doing and what he is spending. It is no longer any of your business and you'll be more at peace when you can stop running after his pitiful life.
As I read here I see more and more that there is one gift of being a single parent of small children. I was simply to busy and overwhelmed to spend any time trying to figure out what he was doing. That is said in seriousness, not snarkyness.
Hope you have a good weekend. When I was newly divorced I would take a block of time (6hrs, one day) and conciously make myself think of something else every time my thoughts went to my xah. I would say "Thumper, go do xyz, talk to xyz, think about xyz, read..." Whatever. It worked to a) train myself not to think about him all the time and b) realize how much time I was thinking about him.