Actually, you would use this: "If he wasn’t faithful to his ex, he wouldn’t have lived alone." If you said "If he wasn’t faithful to his ex, he wouldn’t live alone until now." , you would contradict the present with a past participle. "until now" would imply that this event happened in the past, but the words before ... "he wouldn’t live alone" imply a present tense statement. What gets REALLY confusing though, for anyone, is that "until now" could imply that he is not living alone anymore. So what you want to do is imply that there is no change in status of him living alone, and assert the point that if he was faithful then none of this would have happened. So... "If he wasn’t faithful to his ex, he wouldn’t have lived alone." is what I think should be said in this instance. Yes, I edited this several times as I kept reading over and over, ;) I think I got it this time!

Choices 1 and 2 are grammatically incorrect. More information here: https://www.ef.com/english-resources/english-grammar/conditional/ The statement "He has lived alone until now because he's very faithful to his dead wife" is confusing. The words "...until now" imply that he has recently remarried (or the common-law equivalent) which may not be your intent. The word "faithful" probably means "devoted to the memory of" but could also be understood as "not adulterous while she was alive." Here is my best guess at your meaning: "He lives alone because he's devoted to the memory of his dead wife." or "He has lived alone because he has been devoted to the memory of his dead wife." Type 2 conditional. "If he weren't/wasn't devoted to her memory, he would not live alone (now)." Type 3 conditional. "If he hadn't been devoted to her memory, he would not have lived alone (so long)."