consider contacting a private detective, may be worth having that evidence for the D hearing. But I wouldn't disclose the evidence unless you had to. Don't use it to get revenge, only if needed to protect your son.
Overall, glad to see you seem to be doing well, going forward is slow, but you have a lot of history that you are moving on from, and even though the way it ended $ucks, you still had a lot of happiness and it takes time to mourn the loss of that. One day at a time.
M - 9 1/2 years 5/5/16 - Bomb drop - 3 week EA 10/31/16 - We sold house 01/10/18 - D Finalized