It is an emotion that can have physical side effects! I think that as you develop your own emotions your idea of love and what that is/means to you changes over time. I think we have all experienced that first true love and then moved on life to find love in a deeper way as we develop and mature. You can�t really say how you know, as said above it�s a personal instinct. The idea of commitment is accepting that you will love no other the way you love the person you are with, although unlikely, this is why people commit to a relationship and/or marriage as they believe rightly or wrongly that 'this is the one'. Only you will know that.