Cullen is afraid of what he's willing to do for the inquisitor and what he stands to lose.

Tyrion knew, as he gazed up at the dark skinned Martell man that this was perhaps his only chance to spirit Sansa out of King's Landing and away from his father's greedy fingers. Tywin Lannister would have married the girl himself if he felt he could have gotten away with it, and so Tyrion knew his own marriage was no protection to Ned Stark's daughter whatsoever. "Invite her, demand her, steal her--whatever you choose, Prince Oberyn, choose it soon. Else my lady wife shall break into more pieces than the stars."

Dave just wants to be left alone. What's the point of anything when what's broken can never be completely fixed? This is the story of Dave Strider and Karkat Vantas, on the longest journey of their lives.

It wasn't exactly like he could blame Clary for liking Jace. But “I'm hiding my feelings for the guy you thought was your brother so you don't doubt that my feelings for you are genuine” was a little different than “I'm hiding my feelings for the guy I didn't tell you isn't actually my brother and by the way his kiss is the one I desire most.”