One visit to the counselor will not be an indication that the marriage is doomed. The goal of the therapy is to let him realize why he may be feeling this way. Is he experiencing some sort of a mid life crisis, is he depressed, was there an issue of infidelity, is he burned out from his work and parenting responsibilities, does he blame you for not getting along in life professionally (this may be done subconsciously, etc)
Hormonal changes (in men as well as in women) can cause someone to feel a sense of emotionally disconnection. Neurochemical changes as well ex: oxytocin, dopamine, serotonin, etc)
It would be imperative to figure or re figure out what the marital goals were (what the two of you wanted to achieve) as well as pin point your individual goals (what does he believe that he is not getting while in the marriage)
If he did not tell you, you are not expected to guess. A part of having a workable relationship is open communication. You may start by exploring with him what may have been some of the things he himself is in control of (how he lets you know if something is amiss, what queues to give you that you can look for, etc) Meanwhile, during your counselor's visit, see if working on improving couples communication is something they can offer assistance with. In addition to counseling, some couples also work with a marriage coach.
Let him know that you're there for him emotionally and in any other way and ask him to meet you half way in your attempt to reconnect. After all, he has to work on himself as well. If he had been open with you from the start, perhaps things would have not progressed this far.
The Power of Two Workbook by Susan Heitler and Abigail Hirsch (Paperback )
The Relationship Rescue Workbook by Phillip C. McGraw (Paperback)
Why Can't You Read My Mind? Overcoming the 9 Toxic Thought Patterns that Get in the Way of a Loving Relationship by Jeffrey Bernstein and Susan Magee (Paperback )