I think this happens on both sides, and to some degree it is inevitable. But there are ways to keep a marriage fresh. They just take work.
It’s also being forced to actually get dressed up if you want to attract someone and get laid.
The fact of the matter is that when people are single, they have a shit-load of free time. And they spend a significant amount of that time working on their “brand” (for lack of a better term) so as to attract a partner. Clothes, hair, going to the gym, planning all sorts of fun parties and outings.
Marriage is also mostly a shit-load of shared chores. Particularly if you have kids. Doesn’t leave much time for planning fancy dates with the SO.
Also, the fact of the matter is that you and your wife aren’t 26 any more. Everyone always fantasizes that if they were single, they’d be living in some sweet loft in SoHo (or whatever your equivalent), partying every night and banging all sorts of chicks (or dudes). But there gets to be a point in life when you go to the bar and instead of seeing a wild party, you see a bunch of sad middle-aged drunks and losers./
Your wife isn’t preventing you from fucking a bunch of college co-eds. She’s the one preventing you from sitting in Appleby’s by yourself.
Bawahahaha
Win… 
My Mother’s Mother told her that if her husband wanted her to go somewhere with him, to do it because it won’t take many 'No’s before he will find someone who will.
My Mother wore her wedding suit on her 50 wedding anniversary.
The only times up until the day she died that she could not wear it were the 8 times she was pregnant. 
My 70-year-old mom is still pretty close to the same size she’s always been. Both of my younger sisters outweigh her by a large margin. Mom had three kids, the older of my sisters has two, and my youngest sister has had none. Both sisters were quite slender when they were younger.
My Mom wore her birthday suit. The nursing home staff were not pleased…
[sub]The above is a lie, it did not happen. Would have been funny though, assuming I didn’t see it.[/sub]
It would be a sad commentary if any of us in our forties were no different than we were in our twenties.
Of course everyone changes. Your best hope is to look for somebody who seems like they really get that.
I don’t think the thread is about people who change as they get older.
It’s about people who drastically change within a short time after getting married.
For example, I know three women who went from rather attractive to well into obese within about 4 years, because they gained an excessive amount of baby weight and didn’t lose it after.
Frankly, I feel sorry for their husbands.
Yeah, you’re right. Never mind.
Marriage is hardly a prerequisite.
I knew a 30-32 year old woman who was going through the office - while on her third marriage.
I left that job and moved on - ran into her on the street (chilly day) and she immediately whips open her coat to reveal the “thin” version.
Having passed on my chance at her (I don’t do marrieds - I’m nobody’s side dish), I was free to comment: “So, back on the market again?”. She didn’t much like that. Turned out to be true.
Knew another woman who, at 18, was probably hot stuff. Her “boyfriend” dumped his first wife when she got “too old/fat/whatever” and hooked up with her.
She turned 30 and put on 20 pounds. You’ll never guess what he did - he found another 18 year old bimbo. Poor Lynda didn’t take kindly.