When it comes to working out how long marriages will last, I always think of a famous British TV presenter, Bruce Forsyth. He married Wilnelia Merced who was over 20 years his junior (if not 30) in 1983 and everyone expected them to split within 5 years*. Instead they were still happily together when he died in 2017 (and there was never any suggestion either of them cheated either). It just goes to show you can’t tell which relationships will succeed from the outside.
*She was a young and extremely beautiful ex-Miss World, he was rich, famous, substantially older and not traditionally good looking plus it was his third marriage. Conclusions were jumped to.