No matter what Cullen tries telling the others - tries telling himself - he does not worry when Lavellan is out on missions.
He's glad she brings Bull with her, because it's not that she's not capable - Maker knows she can handle herself in a fight - but because he's trust in Bull's skills and Bull did after all appoint himself as her bodyguard.

If anyone asks is he worries about her, Cullen blushes, shrugs it off and claims it's because she's the only one who can close the Rifts.
Leliana and Josie knows better, but doesn't let it on, while Cassandra smiles knowingly at him and lets him know she approves without saying a word.

Cullen's never had any reason to trust mages, and finds himself not knowing what to think of Solas, Vivienne or Dorian, but seeing as Bull trusts Dorian - enough to let him into his bed at least - makes him less distrustful towards the Vint than he was in the beginning.
He doesn't know what to think about Varric - he counted Anders as a friend after all, and Cole is not human and therefore dangerous. Sera is… strange to say the least, but based on the rooftop talks and cookie-baking, it seems Lavellan trusts her.

He'd be happier if she brought Cassandra along more often, although it saves him from embarrassing himself by asking about how it went while they were away and was Lavellan hurt and did they run into any trouble or did the Seeker learn anything new about her or did Bull make a pass at her because if the qunari did then…..

Cullen hates the was Cassandra looks at him; hates himself for being weak enough to ask her but not strong enough to ask the Herald herself.

But Cullen can admit to himself that he would do anything to be out there with her; to fight alongside her, to keep watch over her at night, to have her back as she would have his.

It takes weeks, but Cullen finally admits to himself that he loves her.