I actually think Cullen will have very few occupational doubts now, he's been around the block, seen and been involved in so much. I see him as battle hardened & confident with most things military but I don't see him as being cruel, single-minded or unfair. I think he will have the knowledge and confidence to stand by his decisions and opinions.
In his personal life, I see him still being reserved and quite awkward, I could imagine him spending a lot of private time, re-living in his mind, conversations, flirts etc with his LI, breaking them down, mulling over every word or mannerism just to convince himself that it's real.
This is sorta what I expect. I don't think he'll be blushing and stammering (nor do I want that). But I expect him to have had little experience in the serious relationship arena. So I'd love for him to be super confident man in the War Room, and then constantly second guessing himself in his relationship with you. Then, watch he's constantly going to Varric for relationship advice, but Varric sometimes just f*cks with him, because he can.
Inquisitor: **ACHOOO!**
Cullen: Um, so... you don't actually like Andraste's Grace? Varric said they were your favorite.
Inquisitor: Well, it's very... ah, ah, ah, achoooo!! pretty, Cullen. *sniff* But, I'm terribly allergic.