Could he go, but stay in the background (and not necessarily go to the wake)? He was part of the family, he loved her, they had children together - he has some "right" to be there, IMO.
Gness, I anticipate the same problem for me in future - I'd like to go to my ex-FIL's funeral when the time comes, but ex and I have been apart for 25 years. I don't want to cause waves but I am still friendly with the rest of the family.