You can point out what you have observed to him and let him know that you care about him and are concerned. A lot of the things you mention sound like symptoms of depression. Has there been something going on in his life that could be causing a lot of stress or is otherwise difficult to deal with? That would not be a prerequisite for depression, but if there is, then helping to reduce the stress could help a lot. It sounds like maybe he could be experiencing a "midlife crisis."

Above all, keep letting him know that you care. Be there for him and support him as you can. He has to make the choice about what he is going to do about this, and while counseling could help, he ultimately will have to work through it himself.

<font color=green>"Loneliness does not come from having no people about one, but from being unable to communicate the things that seem important to oneself, or from holding certain views which others find inadmissible" Carl Jung</font color=green>