Yeah above poster is right. I did it exactly the same way and second I chose templars and I havent got him yet and at the point before skyhold, no spoilers.
Odd....On my first playthrough I kept socializing with Dorian and mother gizzelle and even went Templars and she still showed up, wanted to have to give the letter over to him and as i did in one of my recent characters I defended him but still promised to give the letter and still gave the letter to him and blah blah blah blah about his father.
Hmmmmm.....I know Dorian has a couple WAR TABLE ONLY missions (One in Fereldan and the other in orlias) and has a couple missions where you have to explore but I believe one of his explore and kill stuff is after the whole (spoiler free) thing then you'll get a mission called "ONE LESS VENETORI" where you have to take Dorian out to kill Venetori soldiers because of (spoiler free) after the (spoiler free) meeting.
