how u could know that aperson is totally inlove with u?//?

Question

really i don't know how?

Answer 1

For sure? Ask him/her.

If that's not posible to do, then you'll have to observe more closely.

Is that person doing anything special to you and not to everyone else?
Is that person always around you?
Is that person always trying to get your attention?

Above are few examples, and it doesn't apply to everybody.
Some people are not very agressive. So the way he/she approch you may be different.
Is that person seem kinda shy or less talkative with you but not with other friends?