When you don't need to ask the question any longer :)
when he asks YOU for a cuddle after se.x
I haven't the foggiest and have been married three times. Men to me are a puzzle, wrapped up in an enigma, wrapped up in smelly socks. Let me know please if you figure it out
If you start talking about planning the children and the house and all that and he doesn't run away screaming, then he just may be serious about being with you.