At some point QS many of us end up having to go it alone... It's painful, but managable... You just need to focus on the goals here... which is YOU with a healthier lifestyle... marriage is ideal IF your partner is willing to eventually offer that... but if they arne't at some point you have to say
"OK, I can do better than this..." YOU decide when that point is... If there are others willing to fight while you aren't willing to, then you aren't there yet... This is often when a lot of people give up is when they have to go it alone.
The problem is they are chasing the wrong thing - you want a healthier lifestyle... that can be a monogamous spouse OR hitting the dating circuit again...we don't know what it is yet... But you need to stop worrying abotu what your wife is doing...