1. When your spouse mentions that the old boy/girlfriend they once told you about looked them up out of the blue, the "Check Engine" light might have just come on in your marriage. Take them out to dinner and pleasantly ask lots of open-ended questions. If you don't have a weekly "date night," now's a really, really good time to start.
2. Old flame or no, consider building a bit more quality time into your marriage - your spouse's idea of quality time. If you don't know what that is, ask.
3. If their idea of q.t. involves physical affection, don't roll your eyes or express exasperation or disgust. Do not announce that it's not important. If you don't enjoy it any more, confide that to your doctor first. In particular, avoid disclosing to your spouse that you never really did like it, even if that was the case. Oh, and don't use the word "addict," even in fun.
4. If your spouse has always been the quiet, patient, long-suffering type, but begins to appropriately and courteously verbally convey his or her wants and needs, especially in connection with 3., above, that would be what's commonly known as "a clue."
5. If your spouse requests you both go to counseling, the list of recommended responses does not include refusal, especially if 4., above, has already occurred.
6. If, after several unsuccessful attempts to discuss it with you, your spouse drops the topic completely - especially if they finally "see it your way" and quit making overtures - any feelings of relief you feel might be short-lived. In reality, you may have only weeks - maybe months, if they love you - before they decide it's easier to live alone than to endure constant rejection.