It may be time to cut your losses and move on. Consider your options.
An old acquaintance may hold the key to your success today. While you may need their help, keep in mind that they're not a true friend, and not someone with whom you should share potentially damaging gossip or intimate secrets with. Keep it professional and amicable.
You can't win every argument, nor should you. Don't let an egotistical desire to win consume you; it's bad for your working relationships and your frown lines.