There are seasons in every long term relationship where something like this can happen. It can be entirely his fault, not his fault at all, not her fault.....it could be deliberate. She could be upset at him for something else. She could be having awesome sex with him once a week, but to him it's not enough. She could be making herself have sex with him merely that seemingly often to her and it's rare for him.
There is a honeymoon phase and when it's gone, the one with the still active sex drive is very disappointed. If everyone chose to leave their spouse on these terms alone, we've have nearly a 100% divorce rate.
Sex isn't that big of a deal until you aren't getting any. But it is not the entire formation of a relationship. It can be the biggest thing in your life going wrong. She could be having sex with no enjoyment what-so-ever, or merely making herself do it once a week and still enjoys herself but it's hard to get in the mood.
The guy might be wanting her to do things she's not really wanting to do and that could be turning her off and making her surprisingly *lose* the handcuffs he bought for her.
This could be entirely benign, but based on the efforts he's put out to try to get her to put out, he might be turning her off by trying harder. And like someone said, if you back off entirely you might never get laid.
It's a delicate issue, i suggest non-religious counseling, for yourself, for her or together. Or wait and see and give it some time. Maybe backing off for a little longer might do the trick.
I've gone through months of zero sex drive. My husband rarely approaches me for sex, but is 98% of the time willing to have sex if i approach him. We always have a good time. But sometimes we had no sex for months at a time. Never years at a time. But he never was the one with the high sex drive so it wasn't as huge of a deal for us. He'd jack off like once a month when we didn't do it for 3-6 months. But we didn't just not touch one another. I might have been going through a crazy alien transformation of emotions and hormones, but i still jacked him off, gave him oral sex or let him hump my leg if he wanted to.
It was rare that i turned him down during that time. Had he left me for that reason, we'd be having to explain a lot to our daughter. We worked through it and sex once a week is average for us some weeks. As long as we are functioning in other areas of our relationship it is a good sign we are still doing fine. If we are fighting constantly, then every part of our marriage is growing cold.
Sex isn't the glue that holds everything together, one day you will be very old, very feable, sick and you might not be able to have sex, or the other person might not be able to. You can still love each other very much and still be intimate without intercourse. People do it all the time.