It's easy to turn this question around: Are you saying that you should live your life beholden to someone else just because they're supporting you financially? Isn't that servitude?
You're beholden because you're married, not because you're a slave. You have a choice of divorce, nobody is stopping you from leaving, being financially dependent that doesn't justify cheating on your spouse.
Ten years is a long time, and people change significantly. Think drug abuse. If your SO is strung out all the time, and you have no ability to support yourself, what would you do?
Unfortunately this isn't a corner case. It's a sad but common story.
I'm not judging, I get every situation is different. It sounds like you're referring to a specific incident, 10 year+ relationship, things change, spouse is a drug user.
Sounds awful. My opinion is still that one should leave the relationship ASAP, regardless of how difficult it is financially. Support groups, family, part time work, driving uber, whatever it takes. I think it's unethical to stay in a relationship for financial security while trying to find a replacement.
Even if there was emotional or physical abuse my answer would be the same. Exit the relationship, find support, don't have an affair.
> . If your SO is strung out all the time, and you have no ability to support yourself, what would you do?
You should work out your issues, remove the things in your life that are causing you harm. (That relationship) Then date later. Moving from one bad relationship to another is a huge redflag.