It is clear that church commitment is about him, and not you.
But you have been married long enough that you can feel free to go to separate churches. There is no scriptural mandate that the whole family needs to find spiritual support in the same place. It is a cultural expectation, and nothing more.
Fight for the spiritual growth of your son. Stand up for your right to have a life of your own, doing things that you value. Otherwise your entire life will turn into whatever he dictates. I am not suggesting you oppose him, but just assert that you are a whole person with interests and goals.
There are many potential reasons that come to mind, some of which people have listed. You can work with him on this in a subtle way, not accusing but making recommendations. For instance, remind him that he tends to panic every half year (or whatever increment) ... so he could plan for that to happen. In his mind he might see it as viable reasons the church was at fault, but you can say, "If you know you're going to be dissatisfied every [half year], then just tell yourself you will be at that church for only half a year, and then leave."
People who get angry or fearful will often disrupt things for others, trying to draw them into conversations on blame. That can be useful if there are real problems, but not if this is a chronic internal dissatisfaction.
Possible reasons:
1. Being an analytical person who observes what goes on, and finds details to fix but has not authority to fix them.
2. Noticing like peers have different occupations and interests, not relevant to his life.
3. Fear of not being able to compete on that playing field-- a lot of people throwing around scriptures or looking super-spiritual.
4. Past memories of feeling disempowered in a church -- maybe even just flashbacks of parents fussing over clothes, teachers making them feel outcast, kids in cliques. If those memories are triggered, he might assume this church will offer the same discomforts.
5. As you say, standing by himself, expecting others to approach him. Everyone has to work at making friends, or it will never happen.
6. Seeing you having fun in groups and making friends, maybe being happier there than you are with him. Jealousy of the church being better at meeting your emotional needs. (In your mind there is probably no comparison.)
7. Seeing you as a different person than he expected, than he wanted you to be. When you are together at home, you are the person who knows where the socks are... when out in public, you might shine and show up a lot of expertise that makes him feel like, "Who is this woman?"
8. Feeling of being trapped, locked in to a commitment, obligated to a group of people.