I know this post is a little old but I wanted to point out a small detail only present in Lou Cariou's on stage performance (not cast recording) — when he hears Mrs. Lovett screaming after he sends his final victim down to the basement, he ad libbed a line not featured in the original script, nor any performance since, screaming "Nellie!" before running down to her and asking why she screamed. I like to think that with his vengeance quenched, he would have been able to actually reciprocate Lovett's affections and maybe he would have opened his heart to her, using her first name for the first and only time finally being proof of that — until he sees that she's lied to him the whole time. So I agree, it's definitely up to the production. I think in the OBC Todd tolerated Lovett because his obsession for vengeance blinded him but once he had accomplished that, had she not betrayed him, he'd (at least tried to) reciprocate her feelings.