I think you're looking too far into this.
We know a few things here
Dabbid REALLY wants a bond
The Sibling doesn't want a bond, and has been very clear about that.
The reason the Sibling could influence Dabbid was due to his impairing
The Sibling told Dabbid that a bond could heal him.
I think the likeliest thing here is that Dabbid asked how the Sibling was talking to him, and the Sibling responded by pointing out his mental issues, at some point Dabbid asks if it can be healed, and the Sibling says yes. No promisise made, no hints, no implications, but Dabbid assumes that is the terms of their deal, because that's what he wants.