I hope you don't mind me replying to an older post; I found this interesting because I hadn't thought of that possibility (Merlin reminding Arthur that he could just have let him go ahead); it's true that it must have strengthened their bound. On the other hand, Merlin solidified Arthur's prejudice against magic that day, and people with prejudices often aren't rational, so I think that it's not certain that Arthur would be - though maybe that's giving him too little credit? And there's always the possibility that Merlin wants something evil but different from Morgause...
(I agree about Igraine being real.)