I do not think that you can equate masturbation and homosexuality. My guess is that something greater than 99% of all males masturbate.
That doesn't matter. 99% of males lie, commit adultery in their hearts, etc. too. Just because lots of people commit the same sin, does not mitigate its sinfulness.
And to homosexual people, it is as natural to lust after a fellow male or fellow female as it is for hetrosexual people to lust after the opposite sex. It does not matter how natural it is to other people, because naturalness is beside the point.
All sin is 100%
unnatural when we compare ourselves to the innocence of prelapsarian Adam and Eve. Regaining that sinless innocence is our first step to theosis. "More" or "less" means nothing. It's
not, so the degree only indicates the amount of struggle it will take to overcome.
In the latter case, it would be nice if the wife said “I’m sorry dear, but I am really tired tonight” you could reply “No problem honey, I can take care of this myself”.
Perhaps, but even that is not in line with the basic asceticism of Christianity. We don't just go and fulfill every urge that comes along. If a husband is feeling aroused one night but his wife is not interested, then the husband has to live with it—not go and "take care of it" himself. Just like we don't go and eat every time we want to, or go and flirt with every attractive person we see.
As it is, however, it seems that the only acceptable way to have sex is within the context of marital copulation.
Correct. All other forms of sex, including autosexual activity like masturbation, are missing the mark of why sexuality exists.
And yet, there are even those who would say that is “dirty”, particularly if either of the partners actually enjoyed it.
Because whether we enjoy something it is not the standard we hold ourselves to.