It's a pretty good deal, really.
The majority of the time, John serves his unit as a doctor. He gets a lot of surprised comments about how good a doctor he is, to which John just rolls his eyes. He’s combated the stereotypes about omegas as dumb, flaky sex machines all his life. But an omega's nurturing instincts give him a great bedside manner, and the innate tendency of betas and alphas to find omegas soothing results in John's presence being very therapeutic for his patients. He's not above actively using that. He spends more time than most doctors sitting with his patients, talking to them, befriending them, and letting them bask in his scent. He suspects it has saved a number of lives; if not by speeding their initial recuperation, then by providing them with the support and morale to make it through the fight for recovery afterwards.
It’s made him a lot of friends, too. Many of his patients have stayed in touch. He hears from them a lot around Christmastime.
But then there is that minority of the time.
Here is the thing about being an omega: it sucks.
Every three months, John's biology completely flakes out. He becomes useless for a good week and a half. Sure, he's useful most of the time, but calculate his absentee rates and then tell him, who the hell would hire that?
Even worse, for that week and a half, John is literally constitutionally incapable of thinking about anything but sex. Oh, he can roughly manage to meet his basic needs—feed himself, shower, get up to use the toilet—but those activities are carried out with the groggy half-thereness of a midnight trip to the loo. He's lucky if he can manage to walk straight. And he is in constant...he'll call it pain. It isn't, precisely, but it is a need so intense that it's like a pain. He couldn't explain it to anyone who wasn't an omega.
Although he did once meet a submissive alpha who liked to be edged to the point of insanity. They compared notes; John suspects that man got it.
In any case, he spends that entire week and a half ready to drop to all fours and/or roll over on his back with his knees in the air at a moment's notice, any time he meets an alpha. And he wants to meet an alpha; oh god does he ever want to. No one who isn't an omega can ever understand the strength of will it takes at every moment not to simply walk out into the street and instigate his own gang rape.
But that's the thing. John could have all the sex he wanted (and he wants a lot of sex, for that week and a half)—with total strangers, who may or may not be clean, who may or may not be decent people, who may or may not be inclined to carry him off and chain him in their basement or sell him off to a brothel in Thailand with his tongue cut out so that he can never tell anyone who he is.
Well. You never know with alphas.
Omegas who find an alpha they trust—whether it's a life partner, lover, or even just a friend-with-benefits arrangements—are lucky. There are drugs to prevent conception, but the drugs to prevent heat don't work so well. They tend to function imperfectly at best, and the side effects can be beastly. It comes of having your system awash with those levels of hormones (fucking adrenaline; it screws up everything, except when it's the magical cure-all). So essentially, an omega either lucks out and finds an alpha he can trust who'll fuck him through the floorboards for a week and a half, or else he's stuck riding out the biological Chernobyl leveled on him by his own body. Every three months.
It's just about enough to make a bloke want to get spayed.
The army, though. The army is bleeding magic. John is placed with a unit he can care for. These men have his back, protect each other, and on occasion, John has saved and defended them in turn. He's one of them. They are his. The bond is more than just trust, and it's more than he ever hoped to have with even one alpha.
And when that three month mark rolls around, and John is relegated to a week and a half of helpless, desperately begging writhing on his cot, there isn't a single minute of that time when he isn't being gloriously covered and mounted by a gorgeous, fit, caring alpha. They take turns on him, bouts of athletic sex followed by a half hour to an hour at a time of slow, sensual knotting. It feels amazing, his body spread open, weighed down and overpowered. They service him till he's rippling with sexual pleasure, never quite sated but momentarily content with their occupation of him. Hell, they wait on him hand and foot when he lets them, towelling him off, bringing him water, cleaning and massaging him, unless he demands that they let him up so he can get his own damn food.
It was difficult to take a shower, at first. They all discovered more or less at the same time that John naked, wet, and smelling ripe was in fact irresistible. He couldn't finish washing his hair without being pushed down and taken. But after the third time he was interrupted, he shoved the soap into his partner's face and told him, "You want to fuck me, then you finish the job."
They've made it into a game since then. The first one who breaks and goes for him gets handed the next gruntwork task their unit is assigned to. John loves this game, because it means he hasn't had to do inventory since he deployed.
When he sleeps, he sleeps in a puppy pile, friends and comrades tucked around and on him, pulling him close and protected against their bodies. They'd never dare try it outside of heat—the time he sat down and described in precise detail the surgical procedure to quickly and safely neuter a man made a lasting impression—but while he's in heat, he's vulnerable, and having his mates around (in the friend sense, though he supposes also technically in the other sense) feels safe.
The arrangement wouldn't work anywhere else, to be fair. Alphas are territorial. But the extremely close quarters of a military team in the field means that everybody smells like everybody else. They register as family, as pack. They all own each other.
Civilian omegas are horrified when John tells them what he does. To them it sounds as though he's some sort of sex slave. They can't quite wrap their minds around his explanation of how that's the furthest possible thing from the truth, so these days he doesn't even bother to try.
As far as John is concerned, he's in the uniform for life. He can't imagine belonging anywhere else but here.