I always fantasized about getting married to a merely plump woman who began to really pig out on the honeymoon cruise, becoming noticeably fatter as the week went on. And once home, the gain continued, with her being perfectly content from then on with her constant over eating and growing weight.

She wants you fatter.
You seem open to the idea of being fatter.
So start over eating and get fatter!
Bring fattening edibles into the bedroom and ask her to feed you as you're coming on. Or feed yourself right there before her as the mood is heightening.
Talk about how hungry you are, asking her what you might snack on. Or, if you can, always try to be eating at least a little something when you're together at home or in the car.
Buffets, buffets, buffets.
In any event, if she wants a fatter you and you want to be a fatter you, give her a fatter you.
Fattening up is as easy as pie, ice cream, and triple helpings of both as often as possible.

Heavy cream, or sometimes just cream, is drinkable while whipping cream is edible.
Relative to gaining, each is about the fat/calorie content. The more calories you can consume from them, the more, and sooner, you'll fatten up. Both give you lots of fat calories without having to consume too much volume, meaning lots of calories per individual feast.
Something dairy based called Boost is sold here in the United States having about 500 calories per pint, I think. With a little practice, you can drink 3000 calories or more per sitting. Gainers here are turning to it to speed up their fattening - and it seems to be a very effective product for that kind of end use.

With some women, a lot of the weight gain goes to the breasts. With others, when extended pigging out occurs, another part or parts of the anatomy are the beneficiaries.
I like it when everywhere on a woman expands with the added pounds. An overload of erotic flesh all over is where it's really at, though the other body types, where the additional fat is more concentrated in certain areas over others, have their definite sexual attraction too.

Congratulations on closing in on your goal! Exciting, isn't it? And now you're only about a year away from finalizing your gain with lots of wonderful overeating to look forward to.
Once the weight is achieved, an expensive, filling, celebratory meal out with your significant other is a must. If you arrive home afterward stuffed full to 334 pounds, I'm sure he or she won't be put out in the least.
But will 330 be enough for you? Might you want to go further - or is this current decision firm?
Saw your photo and you have a very pretty face, the type those added pounds will be kind to.
So keep enjoying all that sensually erotic flesh - with the keen knowledge there is a lot more of it soon to arrive.

Seems to me if you are into this and seriously want to gain as a life style you need to find out if he's truly OK with your interest. The best way to find out is to be up front and honest about it with him. He ought to have the option of either accepting or rejecting your fetish if it is important to your sex life and the relationship is serious - and it very much sounds like it is.
Of course, you're afraid of losing him if he's either not into it or unwilling to put up with it but if you end up together and later decide you want to be open about it and he doesn't approve, he may take off then, perhaps leaving you after having started a family.
Shouldn't he know who you really are, and you him, before you either marry or permanently commit?
The other option is to keep your interest hidden for life. I'm sure plenty have done, and are doing today, just that.

My fetish does not include weight gain for me. I like it just on women.
No idea how typical that is in this community but my own fat does nothing for me.

Each of your arguments against are strong & reasonable. And from your response it sounds like chances are a purposefully significant gain is not in your future - and that's OK.
I do wonder what percentage of people sexually stimulated by their own fat never take the plunge for the same reasons you haven't? I expect a very significant portion keep this particular interest forever in the closet, never seriously considering indulging because of all the stigma's attached to it.

Sat close to a woman at a buffet once who was so fat she was clearly in her wheelchair because of her massive girth. Guessing she was close to 600 pounds and watched her eat her heart out all night long. Part of a family with lots of fat women, her younger sister, though maybe only 300 pounds, was a very eager eater and was certain to fatten up more if she were to keep that pace up. Watching multiple fat women eating all they can with gusto is a beautiful sight.

Just keep the food coming. If she enjoys over eating at all, some added weight will come naturally. And if you focus on her fat while making love, or even just when cuddling, she'll get the idea you're turned on by the softness of her flesh, hopefully making her more accepting of her body being overweight.
And if she gains, something that will increase your sexual libido as her weight moves up the ladder, she'll very likely enjoy the added attention and realize she can get away with really letting go.