Kaidan wondering whether or not to tell Shepard he loves him. (dinner date)
On my whole Mass Effect playthrough, I didn't decide on a love interest until this event. I like the thought of Kaidan coming out with his feelings at this moment, rather than being a love interest at the beginning in the first Mass Effect.
(My headcanon) He probably disposes/hides the rose as soon as Shepard approaches, deciding not to tell him. Then eventually builds up the courage to actually confess his feelings later on in the conversation.
( Sorry for the horrible painting job. My work is always so sloppy and sketchy. I try and fix it, but it only makes it worse; so I clean it up by vector/woodcutting it.