Anything exciting you wish to do with a stranger, go do it with your spouse.Spice up your marriage, avoid alcohol and places of casual interactions. "The old flame" This could be your ex, the man/woman you had a child with but broke up, someone you used to like, or you had sex with in the past.The truth is, many married men and women don't get appreciated at home.To protect your marriage from being destroyed this way, appreciate each other, make your spouse feel like a hero, look at your spouse in an admiring way.This is the toughest affair to break because it makes the man feel good as a hero.Married women also fall prey, especially the successful ones. The man makes her feel good by looking up to her and she keeps supporting him especially financially and giving him her body.
You get too comfortable with this friend, it could be your spouse's friend.
If that is difficult, then talk to a reputable spiritual leader or a professional counselor or someone of the same gender as you; not someone of the opposite gender who can easilly get close and feelings emerge, distracting you from working on your marriage. "The Neighbor" David, a man after God's own heart fell this way. Watch yourself, so that you don't fall for that neighbor hanging clothes outside on the line, washing the car, bending while doing house chores, walking in a loose leso with no bra, dressed in shorts or a vest showing muscles.
Watch out for that neighbor who comes to visit and gets cozy in your home, that neighbor that is within reach when you are the only one at home.
Most of all, be a hero at home, to your spouse, your children. "The one with a shoulder to lean on" This happens when you start running to another person, especially when your marriage is facing issues.
You get that one person who is not your spouse you cry to and vent to, you become emotionally attached.
Protect your marriage from this by knowing that once you get married, friendships have to be clearly defined.