Tunneling isn't the problem. This isn't a tunneling story. It would be similar if the tunnel were a ski mountain, an office or a drug den.
This is a story of escalating isolation. He's isolating from society, from people who care about him and whom, we presume, he cares about. (Or maybe not. Maybe he gets along fine at work and at church, and is simply uninterested in his SO.)
I'd say this is about his girlfriend not liking that he's isolating from society. (Which, of course, is a perfectly valid preference of hers.) There's lots wrong with society; the choice to mostly disconnect from it is a reasonable one for many people.
This is a story of escalating isolation. He's isolating from society, from people who care about him and whom, we presume, he cares about. (Or maybe not. Maybe he gets along fine at work and at church, and is simply uninterested in his SO.)