I'm going to espouse a very unpopular viewpoint and say that the therapist may be right. Not that a diapering choice has anything to do with the health of a marriage, but that thinking about, talking about, buying, and so on may be becoming too important to you. (Here throughout I use the collective you, not the OP in particular.)
I mean, face it, if you've found this board and post on it even infrequently, diapering has a pretty high priority in your life. Washing may only take 15 minutes a day, but how about reading this board? Posting? Shopping? Thinking or scheming about the stash and how to revamp it to perfection? You can be just as kind to baby skin and just as good to the environment using prefold and proraps and never thinking another thought about it. But it becomes addicting, and if a marriage is in trouble quite often the addictions, even the harmless ones, must be purged.
If your husband was obsessed with golf, say, spent two hours a day talking to golf buddies and played nine holes every weekend, that's a perfectly healthy, even health-full (because of the exercise) habit. But if his marriage is on the rocks, he'd better give up golf and quick.
There is no question in my mind that cloth diapering *in and of itself* should have nothing but a helpful effect on a marriage. But can you give up all the accoutrements? Can you stop reading this or any other board, stop shopping, pare yourself down so that the only time you're spending is really that extra 15 minutes of wash? If you can, and if you then put that same effort into building your marriage (good grief, think about what relationships we'd all have if every minute we spent on this board could be spent with our husbands!), you may find that "giving up cding" (not the practice, just the obsession) really does improve your marriage.
There's also the fact that the therapist has picked up on cloth diapering being an issue. If it WASN'T an issue, it would never even have been brought up. If a couple mentions power tools, a good therapist realizes that it may very well be an issue in their marriage, even though there's nothing inherently wrong with power tools. But most couples would never even think of them, much less talk about them in therapy, so if they come up it's a red flag. And most couples would never mention diapering practices. So I think it's entirely legit for the therapist to try to figure out if it's a stumbling block to the relationship. If it's not, great. But there's three pages, almost sixty posts, of intense emotion showing that most of us wives do indeed hold it extremely dear to our hearts. If it starts to become more dear, in any way, than our marriages, then I HOPE therapists bring it up.