Hi, Les!
Extending a warm welcome to SongRamp, and thanks for checking out the Writer's Room! Glad to have you onboard!!
As others have said here, this is a really good first post. I saw exactly where you were going with this, but in order for this to be considered "mainstream", I do think a good re-write is in order. I agree with Carl - the phrase "love 'em n' leave 'em" is too cliche and dated to work in today's music scene. And I agree that that particular phrase won't result in much sympathy or empathy from the listener. It paints the singer in a bad light, as if he just wants sex, and nothing more from women. And the phrase "to love someone in sickness and in health is too much responsibility" just kind of stood out to me in a negative way. I think that this phrase would put the singer in a bad light, as well.
For this to be considered for "mainstream" , I think that it's a bit too negative. A well known writer down in Nashville told me one time "the minute you go negative, you're dead in the water." Positive messages in songs seems to be the current preference in mainstream songs these days, especially from lesser known to completely unknown songwriters. Established writers with a track record have a better chance of getting away with it, because of their success.