Fristly, i just like to qoute a movie:
The Oracle from 'The Matrix'
I wanna tell you a little secret, being the one is just like being in love. No one needs to tell you you are in love, you just know it, through and through.
I'm 21 and theres been a few times i've thought i was in love, but mostly it was just me desperate for a partner -- and the times i did have someone you could consider a partner it felt good but didnt really last.
I'm now in a relationship (sadly long distance) with a wonderful woman whom i intend to spend the rest of my life with.
Only you can say when you're in love or not.
Quite a few times (icluding my current relationship) i've seen couples grow apart or have a fight.. then after not having the other person for a while it feels amazingly incorrect and when they get back with their (ex?)partner it feels like getting air after almost having drowned.
Making promises like "i'll never leave you" are to me, like saying "i'll never get hit by a bus"... you cant see the future so dont promise something you cant garuntee. For Example: (hypothetical and hopefully not the case) but what if you said 'i'll never leave you' and he turns out to be a wife basher?... are you going to stay with him forever like you promised?