It's hard to understand

As mentioned before a person I have known for 50+ years is making a fundamentally bad decision.  He is picking a person that he doesn't really know over his family.  He is leaving his entire family including grandchildren so that he can be sexually satisfied.  I don't understand.  He refuses to see a pyschiatrist because there is nothing wrong with him everyone else is wrong.  It is tearing me apart trying to understand this.  Do you feel sorry for him or hate him?  Do you offer him help or write him off? My spell check isn't working so I apologize for the misspellings.