does the title suit you? "how do I know if he/she is the one?"; the one you really love and need. the one who will be your last in your life.
I don't think there are reasons or spesifications to indicate that person. as I said before, love will eventually appear in your life, coloue your days, wipe your tears, etc. and so does "finding" the right one.
when you're faced with someone, then you feel like your heart beats fast, you wanna jump off a cliff just to prove that you're not dreaming, you find no reason to fall for that person, you feel there's something electric shocks you..... then it's the right one. of course, if he/she also experiences the same feeling. hahaha. did I just make you down? :p
but, really. if you're experiencing those signs I've mentioned, don't be too in a rush, probably you've found your right one. don't be too pushy or too happy that you've found him/her. hahaha. take your time. everything needs a process. if then he/she leaves you, don't worry. if he/she IS REALLY the one who is destined to be with you, they will be back to you. no doubt. if they're not, no worry. God has a plan for you and His plan is the most perfect plan for us.
I'm not asking you to give up or hand in into God, but please believe that one thing that you're gonna be fine ;)
please find no reason to love someone and love him/her sincerely. don't be afraid to love someone. it's okay to make mistake. loving wrong person may be a lesson, an experience, and an input for you to not find the one like him/her again. it's much better to experience the mistake before the marriage, isn't it?
I hope love doesn't bring you down or make you fall/tear apart. spread your love and smile! you don't know what are going to happen next! ;)
"We are all a little weird and life's a little weird, and when we find someone whose weirdness is compatible with ours, we join up with them and fall in mutual weirdness and call it love." -Dr. Seuss