It's funny, the one time Teo seems to agree that he was at fault in some way, it's for one choice he knows he couldn't have changed, not with the state of mind he was in back then... but he's not about to make excuses for any harm that it caused.

He wants to argue that Leno is just stubborn and refuses to give up once he's set his mind to something... and that he could easily fail to live up to that trust Teo has in him. Don't worry so much, huh... he has been worrying a lot more, now that he has others to worry about again...

That's part of the reason he can thank the Sage for saving his life, now. Even if he worries and he's failed at times, he's had the opportunity to help the younger wizards grow and watch over them... as well as find some peace with old and new bonds...

"...If that's how you feel, then know I'll be counting on you in turn."

He still feels responsible for ensuring his safety, as well as ensuring he is safe for others to be around... but as friends? That's a different sort of relationship that requires more mutual trust... it doesn't have to be deep unconditional trust, but there has to be some understanding that they'll look out for each other. And he's willing to give him at least that much.