People who have been cheated on - what were the red flags you ignored at first?

I have cheated on him and I'd say one of the red flags had been, sleeping with him way too early in the relationship.

edit/ I mean, if they sleep with you too early from the beginning, there is a great possibility they're easily going to be given elsewhere if circumstances meet.
I've fully forgiven myself now but I think it's a sign of health to take time to dance the love dance.