Had long good sex but finally ejaculation didn't happen. why?

Several Causes: Delayed or Impaired Ejaculation" is a relatively common condition. It may be temporary or chronic, and there can be several causes (anxiety, depression, excessive masturbation, alcohol/drugs, diabetes, hypothyroidism, low testosterone) If he has NEVER been able to ejaculate there may be a physical cause like retrograde ejaculation for instance. Best to see a urologist if chronic problem.