yes, you are correct it applies to husband or wife
A person cannot be COMPELLED to testify against a spouse (but they can if they want to)
“A wife can voluntarily testify against her husband, but she cannot be forced to”
Not to belabor the point but that is not what I said. Spousal privilege can be invoked by either one to also STOP the other spouse from testifying about privileged conversation between the two. Just like it takes two people to be married it takes both people to release spousal privilege.