Partner lost a bunch of weight and I just can’t get into it

I understand that I’m probably going to get a lot of hate and/or mockery for this. And it’s possible I deserve it, but whatever.
Flinging this into an anonymous void is at least something.

My wife (30s F) and I (30s M) have been together for roughly a decade. She was plus-sized when we first met and through dating, marriage, etc. she gained a bit more during this time. About a year ago, she started an effort to lose that weight and quite a bit more. So, calorie restriction, working out, the whole deal. And it worked. It worked so well that she lost a large percentage of her former weight. Being much slimmer than she’s ever been since we’ve been together, she now has a totally different body type and looks/feels like an entirely different person.

I can tell she does like her new body, as she’s long had body image issues related to her weight. I love her and I’m happy she’s doing something that makes her happy.

But there’s a looming, growing problem. I’m only sexually attracted to heavier women. Emphasis on the only. This has been the case as long as I can remember. My wife knows this too. So, in the wake of her transformation, I’ve lost a huge amount of that innate physical, sexual attraction to her. It’s a timebomb that’s now threatening the entire relationship.

I thought that I might just automatically adjust, that because I love her I would just magically change into a person who was into fitter, slimmer women. Or that she’d be the exception or whatever. I think it’s likely she thought the same thing, or maybe that - despite evidence to the contrary - I was actually attracted to her in spite of her body or something.

But I’ve been in a battle against my own biology ever since. The change in attraction is severe. The whiplash from being exceptionally and effortlessly attracted to struggling to find any of it has been jarring and depressing. The closest comparison I can make is it's almost as if she suddenly became a different sex (I’m straight).

I’ve kept entirely silent about this, and all I feel is shame and guilt. It would ruin her to know that all these changes she’s making that she enjoys are directly having this effect. I’m not supposed to say anything. I’m supposed to find her sexy no matter what, right?

And worse, I’m supposed to be even happier, even more into it all. Dismayingly, it’s even expected of me socially. I have to deal with unsolicited comments – often from male family and friends – about her weight loss that strongly suggest I’m now in some sort of heaven because my fat wife finally got skinny or whatever. It’s not surprising that everyone assumes you've merely tolerated your heavier partner this whole time, but it just reinforces that there’s no safe person to be honest with. So I mostly go neutral, and focus on how she seems happier and leave it at that.

"Isn't it amazing? What a change; she looks so good" Yes, it is. Yes, I'm proud of her for reaching her goals.

But in secret everything is far from fine. Every single part of her looks and feels different, and in a way that I’m powerfully turned off by. Different isn’t inherently bad! But this particular different means that she now physically embodies the precise opposite of everything I've been able to be attracted to. Something as simple as physical touch is no longer a reliable source of connection, but instead induces disappointment and anxiety. If I happen to see older photos of her from before I get this intense, dizzying pang, where I’m confronted with how much I miss the experience of being physically attracted to the woman I love.

Our sex life is miserable and continues to wane as her figure does.

I’ve tried intervening to change myself. I’ve tried months of self-reflection to consider if maybe unconscious insecurity on my part could be behind my feelings (there’s not, I just like big women). I’ve tried forcing myself to watch porn with women that look more like she does now, to see if that converts me or whatever. But after months, I still feel nothing. I’ve tried envisioning the situation like it’s a new relationship, to lean into the novelty of it to see if that’s exciting - but that doesn’t work because I wouldn’t intentionally start seeing someone I’m not attracted to (and it seems weird to try!). I’ve tried “changing my thinking” to artificially latch onto some other physical or emotional cue, but it’s still overshadowed by the changes and feels fake as hell. I've tried trying to sexualize something new about the new appearance and lifestyle, but that was too much of a leap. I’ve tried fantasizing (in secret) about how she used to be, but whoever came up with that “everything feels the same in the dark” saying was 100% lying – tactile senses break the illusion. I’ve tried relaxing and accepting that maybe this is just a temporary dip in attraction and that I’ll just eventually emerge from it naturally if I wait long enough. But it’s not happening fast enough.

I’ve spent so much time trying to fix everything in private so that she doesn’t know I feel this way. The last step would be sex therapy to try and convert me or something, but that can’t be done without my wife knowing the full truth of what I’m going through.

She’s noticed the changes in me and in our intimate life. And I’m lying to her. I’m lying to buy myself time as I try to alter myself. It’s life stress, it’s my health, it’s any other BS excuse I can come up that’s a bit more palatable than “you were so hot when you were fat and now I’m just not into it”.

We’re coming closer to conversations about my hormone levels, medical interventions, etc. But of course that’s clearly all BS too, and skirts the real issue. An issue that’s not her fault.

So to avoid that bridge to nowhere, that means I’m on the brink of having an unforgivable conversation with her. I don’t know how we survive it. Outwardly expressing a dramatic drop in attraction is hurtful and taboo enough. But when it’s directly (if uncontrollably) related to something that makes your partner happier? That is just so much worse. So I fear as soon as I'm found out, it will be the start of the end of our relationship; who wants to be with someone who loves them but struggles to find them attractive? Isn't that latter part the lowest bar possible?

Of course I'm happy she's happier, and likely healthier. But after many months, my logical appreciation of that hasn't become a sexual one and I'm stuck.

Like I said, I know sympathy will be low on this because of how we collectively think about and romanticize desire, bodies, all of it. I'm not really looking for any. I just needed to say this somewhere. Maybe someone else out there dealing with something similar needs to see it idk