I think McEnroe had some pretty severe turmoil at that stage of his life. He just couldn't weather that storm. Quite frankly, no matter how tempting it is, it is EXTREMELY tough to be married to an actor/actress as an athlete. I'm not sure I've ever seen one last. Then you add in the drugs and partying... it just goes south really fast. Actors/actresses don't need to really be focused for long periods of time... whereas elite athletes have to be supremely focused... extremely structured and routine. It has to be a marriage made in hell.
One spouse is in between movies and wants to party, go to dinners, go on long vacations, go to galas, go to industry events, go to fundraisers. The other spouse is on the road 75% of the year, has to train constantly, has to be very regimented, has to coordinate strict schedules... and can't be bothered with anything except the sport. I can't even imagine it.