We are both in our late 30s and have been married nearly 5 years - which has been mostly happy.
I did something a little different before getting married, I wrote out and itemized my expectations of the marriage and her. I shared this with her, explained my reasoning, and had her commit in writing to my expectations (she actually negotiated one point with me.) Health and beauty is very important to me so I included in the expectations that she was to was to maintain her attractiveness, health and girlish figure and that if she becomes unhealthily overweight it will be grounds for divorce. Which she agreed to.
A lot of people think that beauty is vain and stupid. But beauty, the kind I aspire to, is a proxy for health, discipline, self-respect, confidence, and dignity.
She's kept her commitment to the extent that she is not overweight (she's maintained a very healthy weight and has a nice busty-petite frame) and is disciplined about eating a healthy diet - she still looks good naked!
However, she has little to no interest in anything that might cultivate and maintain her beauty. I did get her a gym membership once and we attended together (she was a little bored there) - now she says there's NO WAY she'd go to the gym. She hates makeup (she's worn it maybe three times since we've been together). She's not very interested in dressing stylishly (she wears dumpy old clothes far too often for my liking). It's been about a half decade since she refreshed her wardrobe. On my urging she's gone through little phases when she would do very light workouts at home (Yoga sessions or squats in the mornings) but she would quit anytime I stopped reminding her to do them. She walks almost everyday - running errands around town - which I'm sure helps maintain her weight.
I'm a very different story, I'm a little vain and do a lot to stay in shape and good looking. I go to the gym 2-3 times weekly. I sun tan during the summer. I try to keep my wardrobe fresh with a few stylish new items every year. I'm always looking for some new thing that I can do to stay healthy and good looking - which she's not very interested in.
I have talked to her about my disappointment with her disregard for cultivating and maintaining her beauty. Reminding her of the commitment she soberly made. In fact, we've talked about it A LOT - I even put together a cultivating beauty plan for her itemizing the things she could be doing. I've explained to her a million times that she should exercise and challenge her body a bit primarily for her own good, so she can avoid the chronic pain and health issues that tormented her parents for decades.
She would say "Yes, I'm not going to get fat. I'll try to do better" and then she'll put in a minimal effort for about a week. We've fought about it enough times that I've temporarily given up trying to get her to do anything. So now we're not fighting about it, she's doing NOTHING in this department, and I'm quietly angry about it about half the time.
This is incredibly frustrating to me, I see other attractive women out and about and think about how my wife would totally outshine them if she made a little bit of concerted effort. I'd love to go to the gym or do workouts with her, but she'd rather do a movie night at home together. Also, because of my interest in Biohacking, I have access to a bunch of beauty hacks; Anti-aging supplements, fitness equipment, etc which I use and would love to share with her. But she'd rather sit on the bed and scroll social media.
The conventional advice given to husbands in my position is "If you want your wife to be sexy, make her feel sexy" and "Set a good example, do fitness stuff with her." And I have really tried those two things, repeatedly, with disappointing results. The other advice I've heard is "flirt innocently with other attractive women. Let your wife see that other women find you attractive" - This I have not done, seems disrespectful.
And I should share something BIG I screwed up on. A few years back, I would watch p0rn infrequently (a few times a month). Which I foolishly thought she was OK with, then she checked my browsing history and had a big blow-up. She was very hurt. I committed to no more porn (which I've kept, haven't looked at any for nearly 3 years now - including the borderline softcore porn that can easily be found on social media). But the damage was done.
She had betrayal trauma, a common response among women to discovering their partners' porn stash. She acted a bit crazy for a bad 6 months after this. I made a real effort to understand betrayal trauma and what she was going through - reading books, blogs, etc. We arrived at a healing habit of me doing a daily validation session with her; we would cuddle up and I would sincerely tell her how I found her beautiful, sexy - how she was the only one I had eyes for. At the same time, I did some personal transformational work on some deeply ingrained promiscuous mindsets I had - that I needed visual novelty when it came to women. My wife's unspoken expectations of the marriage were that I'd be 100% faithful to her - even in my fantasies and internal world, anything less was metaphysical cheating to her which I first thought was absurd. But applying a lot of mental discipline I've gotten to the point where I only think about her as a sexual being, I don't have a spank bank of random women in my head. With years of diligent commitment, mental fortitude, and hundreds of these little validation sessions we've rebuilt her self-esteem and trust between us. She no longer feels the need to check my browsing history (which I gave her full access to).
Her latest excuse for not keeping her commitments is, the most valid one yet, we lost a child and had a stillbirth earlier this summer. Now she is in grieving and refuses do things like staying in shape or mental health habits (the kinds of things that would actually accelerate her healing). She is convinced that the only thing that will heal her and make her happy again is having a healthy baby (and she wants to rush into another pregnancy). I however refuse to have a baby with a woman who refuses to show me the basic level of respect: making a little effort to be beautiful for me.
Throughout all this we maintained some romance and a healthy sex life. We had kept up doing weekly date nights, which she would get just a little dressed up for (I loved THIS!) In many ways she's a good wife; being thoughtful, helping me with errands, preparing nutritious meals, etc. But she's needlessly resistant to doing the cultivating beauty things that would make her healthier (and me a lot happier!)
I've even told her, let me pick up some more of the domestic responsibilities so you can take the time to do home workouts. And she hasn't changed her behavior. Oddly, she would rather be my "maid" than my beauty queen.
So you're probably starting to see my frustration. I've made it exceedingly clear to her that she is my only source of womanly beauty in this world. I've made a BIG change in my behavior and mindset to align with the very high expectation of faithfulness that she has.
I see my desire for beauty as the flipside of her desire for faithfulness. I have a lot of resentment around the fact that she's done little to reciprocate and make a similar effort to be beautiful for me. I don't expect her to do 90-minute grueling gym sessions like me, but she could easily spend 10-minutes a day (about the amount of time I would spend on validation for her betrayal trauma recovery) doing something that made her beautiful and healthy. But she refuses because it's outside her comfort zone.
Now I'm the one who feels betrayed.