Peter nods, listening and understanding in some way even if his experience with losing someone is more traditional than the Doctor's.

"It's not the same, is it?" He's lost his uncle and in some sense, he's lost Gwen. He knows that he can't date her anymore, can't have her in his life. He promised her father on his death bed that he would leave her alone.

Maybe here, he can find someone to travel with and it won't be the same, but it won't be travelling alone.