Damon pursed his lips. He really wished he could use compulsion right about now. What had this mystery person told her? It would be easier to know what lies to fashion in order to make her trust him again if he knew what truths she was told. For the time being, he was trying to work with part truths, but if she didn't trust him soon, he'd have to get more... creative.
"Lydia, I am an impulsive man," he told her. "I did not think ahead. It did not occur to me that Stefan might become involved with the same family, and once he did, I asked him to help me keep my cover. I told him that I might forgive him for Katherine if he did." He'd never told Stefan that, but it was believable because Stefan really did want Damon back. "He wanted our relationship back, so he agreed to help me."