I've watched my husband going through a similar cycle for the last 20yrs.. He's ordinarily a happy-go-lucky, predictable guy in his routines.
However, ever-so-subtley in the spring and fall-he becomes 'unhappy' all-of-a-sudden. Same as you describe, he can't seem to derive that basic 'joi de vie' anymore. He has attempted to deal w/ these negative feelings by making large purchases that were beyond our means, developing 'crushes' on other women, peeping at pornography. Now, he just blames me for everything. It began to sink through my head that there was no pleasing him, because his unhapiness is coming from inside of him somewhere. He has a very, very difficult time expressing unhappiness or confiding his emotions to me. He's already drawn me out the door that I don't care for him, or wouldn't value his confidence in me highly.
It's irrelevant to him that I love him-he behaves as though I'm not even there for him, before he's even given me a chance.
I did notice over the years that he loves perfection-even to the point of experiencing anxiety when he feels things are not giving that appearance. On another level, he feels if he states all the 'little criticisms' on the road to perfect appearance out loud, he will be looked at petty, picky and/or ridiculous.
This builds and builds and then he plays out the 'don't get mad get even' club. Superficial relationships are what he feels most comfortable with at this point. Therapy was a dud, because he wouldn't open up. When our first therapist suggested the 'signal' method for sexual communication improvment, he wouldn't even try to implement it. It was very destructive. "You can lead a horse to water..." you know.
But-I think you're a exceptional person that you went right for therapy instead of blaming anyone. You've earned my respect, totally.
So many of us were raised w/ repressed rage, or taught that anger in and of itself is the problem. The minute you have to start censoring what you say, you supress your true feelings and have taken on managing the other parties' reactions. Truth is-you can't really 'manage the other parties' reactions, you just make a cage for yourself.
I hope you're victorious in your journey.