[Lacus nods along, not in agreement but to show attentiveness. Of course she can't agree that everything was his fault; his sister wouldn't either, she's sure. But nothing she says will convince him otherwise. All she can do is be what comfort she can be and try, over time, to show him that he deserves good things despite whatever guilt he carries.]
Every time you speak so openly to me, I am grateful for the trust you show me. I would like to help you believe better of yourself, but the past is past and nothing I can say now will make you think otherwise.
[Her smile widens slightly as she tugs gently on his arm.] All I can do is take you for cold sake to try and put a smile on your face, so that's what I will do.
That, and I can promise that as long as I am able, I will always be by your side. No matter what happens.