Marital sex aims at procreation, unity, and mutual enjoyment. Obviously oral sex to orgasm isn’t procreative. Therefore, if you say it is permissible, it must manifest unity and mutual enjoyment. Right?
So we must say that – if you are right – oral sex is a manifestation of marital unity. Suppose that is the case.
Now if you say that oral sex manifests marital unity, let’s consider the case of two gay people in a monogamous relationship. They can have oral sex, too. If it manifests unity for two straight people, then it could manifest unity for them, too. In which case, we would have to admit that gay couples are capable of manifesting marital unity. And then we’d have to say that gay marriage is OK.
That’s the logical consequence of your view. You may accept that consequence, and support gay marriage. Or you may reject that consequence, and change your view on oral sex to orgasm.
The third option is to hold a view that *arbitrarily *discriminates against homosexuals. I don’t recommend the third option.