How affectionate is your wife towards your son? Is she a good mom? Is she warm and kind to other people, just not you? -- maybe there is a resentment going on underneath. Maybe she knows about your poly friend - ?
Culturally, there are differences that have to be taken into consideration. If you haven't done so, you may want to read up on the views of infidelity in the Chinese culture. From what I've read there is sometimes an understanding that it is inevitable/understandable/tolerable, but IF the wife finds out, that is when the husband is considered a jerk! He is expected to be DISCREET.
Your son is only 15 months old -- 17 more years is a looooong time to be miserable. Glad you are exploring some options for yourself.
Formerly married to Sundance
Boyfriend -- Butch Cassidy