Actually, yes, there are instances I feel infidelity is acceptable or perhaps a better term would be understandable. If a spouse is in an abusive relationship and fears for their safety if they leave, and falls into an affair with someone they care about and vice versa, I would hope they'd get out of the marriage, but can understand why not and why they are doing what they are doing. Also, if the couple has an 'open marriage' and relationships outside the marriage are known and condoned by both, well, that's their business and not cheating in the widely accepted sense. I don't see DEK going with either of those scenarios. And, unless they suddenly introduce children, an argument can't even be made for Tina and her husband staying together for their sake. Granted, we've only had one brief scene of Tina and her husband, but what we saw struck me as a marriage where they've grown apart, are living separate lives and aren't really *in* love anymore. So why go through the motions? Why, if you think you're in love with another man, stay with your husband and be unhappy?
And I could go into a whole other rant that would involve bringing up BSG so I'll stop now. ;p