Please help counter my irrational thoughts

As many of you know, I'm divorced.  My ex had been diagnosed with ADHD around 2007 or 2008.  He has issues with money and with honesty, which sometimes overlapped.  Specifically, he wanted to cheat on his taxes.  I insisted that we pay taxes and I actually filled out the forms because I didn't trust him. But now we're divorced, and he apparently hasn't filed tax returns, and apparently he's in trouble with our state's department of revenue.  (I know because the mail is still coming to my house.  It's addressed to him but he never changed his address. I haven't opened the envelopes but it's not too hard to figure out what's probably going on.) Part of me is so relieved to not be married to him anymore.  But part of me, the irrational part, is thinking, "Being honest and not cheating are important to me. If we were still married, I would be making sure that ex-H wasn't cheating on his taxes.  It's my fault he's getting in trouble." 

Talk me off the ledge, folks!  Thank you.