"I know him better than you do," Strange snaps. "I knew him when he was Norrell's spook, spying on magicians and innocent women alike. He'll abandon you as soon as you get in the way of what he wants. I won't."

It's Lambert's childishness and selfishness butting up against every needy thought Strange had and worry that he'll be abandoned by those he cares about. The seated Strange reaches over to grab Lambert's arm in a slightly possessive manner.

The standing Strange winces at this. Giving Celandine a little frown, he turns back towards the two seated and starts to mutter, attempting to dispel the magic.