Is this okay:

Yesterday when I said that in my opinion the only thing James did wrong, was lying and not ending the marriage sooner(so you could have met someone else for yourself) that’s assuming that we both already agree that cheating is wrong and immoral ….


You can't have a comma between the subject and verb. You need a space after "sooner". The parentheses are intrusive and unnecessary. You need a comma before "that's". The ellipsis at the end should be a period instead.