Andrew,
My wife likes me to be restrained behind tight rubber, butt plugged, and wear a strap on so she can get some satisfaction.
It's admirable that you maximize your wife’s sexual satisfaction by complying with her stated requirements. You're doing good work!
Your wife's entirely-reasonable requirement that you wear a butt plug, however, suggests she is psychologically turned on by the *idea* of the plug up your ass since it does not touch her physically. This, in turn, suggests she has something of a fetish for your asshole. You and your wife may be able to take advantage of that in a way that would yield greater variety and increased sexual satisfaction for both of you.
I find it very frustrating to watch her enjoy orgasms while I have to go through the motions.
But on the plus side, you are doing your job as your wife's husband and doing it well, it sounds like, by bringing her to multiple orgasms each time she fucks you… AND you are doing it via the method that turns her on most (evidently).
After my wife has had an enjoyable few orgasms I get to clean up, then I masterbate while my cock is restricted behind the tight rubber. I fill my rubber panties with cum then fall asleep.
What is there to clean up, since... using a strapon, as you do... there is no cum in your wife's pussy after she fucks you. Does she female-ejaculate, such that afterwards, at her request, you lick up her ejaculate from her pussy, thighs and ass?
As for having to satisfy yourself by masturbating after your wife has fucked you, thus filling your rubber panties with cum before going to sleep... that's essentially what many women have to do after their man fucks them, cums prematurely, then rolls over and goes to sleep leaving them unsatisfied (although they may not wear rubber panties). So, that's fair enough.
You might consider suggesting to your wife she purchase a strapon of suitable size and style and use it to fuck you up the ass, thus further increasing her sexual satisfaction by taking advantage of her apparent fetish for your asshole. See, for instance:
Take It Like A Man - Pegging and Strap-On Sex
If your wife obtains a vibrating strapon, perhaps including an attachment that fits inside her pussy, that may enable her to orgasm from the pressure on her pussy while she’s fucking you up the ass. At the same time, you may be able to cum from the rhythmic pressure of her strapon dildo on your prostate. Alternatively, the rhythmic pressure of your wife fucking you up the ass may result in “milking” such that semen dribbles from your cock, thus discharging your prostate without you feeling a climax.
Rather than regarding sex of this nature (including what you described) as “humiliating,” I suggest considering it a perfectly normal way of satisfying your wife’s sexual needs and taking pride in your ability to do so.
—Custer