Re: Our sex life is going to ruin our marriage
OP, I was in a long term relationship with a man who was very much like you are describing. He just lacked passion and skill and no amount of talking or teaching made any difference. He was willing to try, to change, to improve...but he just never did (or could?)
Between that experience and reading a lot and hearing the experiences of others IRL and online, I've realized that he (and probably your wife) just simply wasn't that good at sex. There is no real reason, just a lack of skill, I guess. In my partner and in most stories like this I've heard of, there is also a sort of general lack of passion sexually, and in the rest of life, too. Like sex and other pleasures are just not that high on their priority list, though they like it and do want to have it.
I've never really read any stories like this where the passion lacking partner has significantly improved. However, I have read lots of stories where the non-passion lacking spouse just made sex better for themselves anyway. There were various ways this occurred, but mostly it had to do with self love, self servicing, and acceptance that their spouse loves them and is doing their best.
If she never improves, hopefully you can come to a place like that. I was not able to in the relationship I mentioned above, but I also was not very tolerant and was incapable (at the time) of figuring out how to self love and self service myself into a better sex life.
Remember the goal of feminism: Making sure only alphas get laid!