Asmodeus: Immortals aren’t meant to grow wrinkled and grey. In time, Magnus will come to resent you, until the bitter end.

Alec Lightwood: I’m here to prevent that future. To get him his magic and his immortality back.

Asmodeus: Fine. I’ll restore both. Under one condition. End your relationship.

Alec Lightwood: What?

Asmodeus: You are the source of all his suffering. You make him vulnerable, weak. With you, he’ll never reach his full potential.

Alec Lightwood: You’re wrong. We love each other. I wouldn’t just abandon him.

Asmodeus: Then I’m afraid you will be the death of him.

From Shadowhunters – Season 3 Episode 18: ‘The Beast Within’ (3×18)