Teddy just held onto Billy, waiting for him to speak. There was nothing he could say to make it easier to read about what Billy thought was his mother. Especially because he didn't really understand Billy's overwhelming urge to connect with his soul-mother, and he wasn't sure he ever would.
He could understand missing your mother - there was still a painful, desperate ache in his chest when he got up in the morning and realized she wouldn't be waiting for him with breakfast - but Billy had perfectly good (really nice, in fact, about this whole gay and dating an alien business) parents. Billy had family that loved him. And Teddy, who still couldn't figure out exactly how he felt about his one brief meeting with Mar-Vell, was certainly never going to understand why his boyfriend valued Wanda over what he already had. But that didn't matter. What mattered was that Billy needed him, and he would be there.