Your questions and personal reflection are all valid and natural. All spouses of alcoholics and drug addicts struggle with these ethical questions in the beginning. And it is often the case that drug addicts and alcoholics seek out people who are inclined to sacrifice for others.
But not everyone marries an active addict. Some addictions develop slowly over the course of a long marriage. Or they develop suddenly, almost overnight, in the case of some particularly powerful drugs.
In the early days of life with an active addict, we ask ourselves the ethical questions you are pondering. We have the "space", so to speak, to do so. Because the addict is not so dangerous to us or to our loved ones.
Then as time goes on, and, in most cases, the addict becomes more unloving, unavailable, and unresponsive to his or her responsibilities in the marriage and in the family, the suffering of the spouse increases. Like a volume knob that gradually turns up.
Until one day there is no time for debating the moral ethics of self-sacrifice. Because either you've just been hit, or your child has been hit, or your child has been hurt in a car accident caused by your intoxicated spouse, or all your money in the bank has disappeared and there is no food and an eviction notice, or you have found out about the affair or affairs your intoxicated spouse has been hiding from you, or you have AIDS because of his needles.
As the suffering increases, the moral ambiguities disappear.