Is he the one?

How did you ladies know your guy was "the one" you wanted to spend the rest of your life with? I've heard "you'll just know".....WELL I have a doctorate in worrying soooooo I'm constantly overthinking simple things. Then I get confused...which leaves me wondering. I'm only 20, and I've only ever ever ever had one boyfriend who I'm currently still seeing. When I ask myself:

-Does he make me happy? Yes

-Am I attracted to him? Absolutely

-Do I love him? Yes

But do I even know what love is? Could I be missing out on someone else?? I've never been with anyone else so I start thinking and compare the situation to other things. Do I know what love is? Can it be better than this? Or do I already love someone who makes me happy-why do I need to try other people?