Even if you take addiction out of the picture, some people really feel like they need a partner. My Dad, who was married to my mom for over 30 years, married an old HS classmate he met at his reunion a few months after my mom died. I think they were married less than a year after she died. That's just how my dad is. I know he loved my mom very much and would have given anything for her to still be with him. But she wasn't, could never be again, and he needed someone. Not for me to judge. I think even before the reunion he was exploring a possible relationship with someone local. He didn't run around while he was married--I would stake my life on that one.