Social Media and Married Couples
That incident brings me to a few points I'd like to share (from a married person's perspective)
1) If you're married, there should be no reason to seek out and connect to ex spouses or ex lovers. What's the point? Thinking it's OK to reconnect with an old flame may eventually put out the fire in your current marriage---especially if you have frequent conversations on Facebook or send too many "tweets."
2) If you're single and your spouse has re-married (as is the case with my husband's ex), it's best that you leave well enough alone and make no contact. Again, what's the point? Connecting online will only draw suspicion from the new spouse--especially if you're not connected with his (her) new better half.
4) If you see someone you don't know on your spouse's friends page, feel free to 3sk who it is. If he (she) gets upset about your inquiry or beats around the bush about who the person actually is, you might want to check out that person's page to learn more about them--and a possible connection to your mate.
4) Trust your spouse to do the right thing. You shouldn't expect your mate to have the exact same friends as you do and vice versa. He (she) probably has different interests and will undoubtedly draw like-minded people. But what you should expect is for your spouse to be up front and honest with you about his (her) connections and not have a problem defriending them if you request it.
Married couples have enough to deal with over the course of their lives together without adding social media chaos to the mix. If you respect each other online like you do offline, you won't have to worry about defriending anybody.