It all came from a place of great affection - after Dorian told the Inquisitor about how his father tried to change him, with the use of blood magic, he'd been a good listener, and he'd supported Dorian. Even kept him calm when he wanted to go and give his father a piece of his mind, after the man tried to get his son to meet him unknowingly. Likely to tell him what a disappointment he was, to keep berating him. Lavellan would have kept him calm too, he would have been there - he was there now. And Dorian was grateful for that.
"I still worry, yes," he admitted, tipping his head back a bit, further into the soothing touch. "You're all I have here. Anywhere, really." Meaning, someone who actually cared about him and loved him - even at the beginning, the Inquisitor was supportive of Dorian's choice to join the cause. Others in the party gossiped about him behind his back, they disapproved of him because of where he was from, but the Inquisitor had always treated him better than anyone in his life had before, even in Tevinter where he'd been cast out from for going against the grain.
Was it selfless, to make that choice? Dorian didn't think so, but we tended to be our own worst critic. "I would make the choice again," he said, tipping Lavellan's chin closer, lips curving around his. "As long as you try, vhenan. That's enough for me."