Only you can answer that. Are there children involved? Were you two still friends? Have you seen or spoken to in those 50 years? Look inward for your answer.
I agree with Echo and Toni. I am sorry for your loss. I would want to add... How did/does the family feel about you? And do you need closure?
thats up to you
Need to show your humane face wouldn't hurt to show up. Remember you once shared your life with him and if it means anything? Go ahead and turn up.
I think it is only if you want to pay your last respects to him and if there are no special circumstances that might create tensions between you and your previous family. I mean that my friend in similar situation found a wife at the dating website who he happily lived with after the divorce. And he also came to the funeral of his ex-spouse. But the family was all against her.