I think possibly you are reading a bit much into this. He and I are friends. Good friends, who also happen to find one another rather attractive.

[ At least that is all that Sif is currently willing to admit to, even to herself. Things are a little complicated in her emotional landscape at the moment. ]

He... invited me along to go on a boat trip with him and another lady. Presumably because both he and I call Legolas a friend, and because I was in rather dire need of distraction at the time.