You know when you know.
If you are questioning your love for him and not sure if he's "the one" then he either isn't...or you just haven't figured that out yet.
There is no magical time when you know, my parents knew on their 4th date they would be together forever...40 years later they are still as much in love as they were on that 4th date.
I knew 6 months in with my BF that he was the one. It just hit me, and I knew.
Everyone is different, but if you find yourself questioning things or just unsure....maybe he's not. If you have to convince yourself that he's it, you are going to have a very rocky road ahead of you.
ANSWER THIS QUESTION