Welcome and sorry for your troubles.
First off, did he tell you up front he was married and poly before you became involved? If you didn't know, he isn't the greatest at poly and basically had an affair with you.
Secondly..if you don't get along with his wife your level of relationship will be defined by that and probably limited. You can read my posts as I am in a similar relationship as far as the structure goes.
Hope you find some insight..I wish I had more time. Sorry for the short answer.