@yuvrajsen,
Perhaps try taking a giant step backwards in your own mind, and imagine :
A best friend told you that she is in love with you - but you can't think of her that way - she's just a friend. So you've said "I'm not interested in being your boyfriend - I would prefer to just be your friend"...
...you were rather uncomfortable with having to tell your best friend that - you hate hurting feelings. You don't ever want to have to feel like that again, so you decide you both need a bit of space in order for things to settle down to a comfortable friendship level again...
...but instead...she keeps constantly sending you text messages...no matter that you never send one to them first. Would you start to worry that you will have to have that uncomfortable, awkward and terrible conversation again?
...so you would you shorten your text replies? (you never send the first text, because you want space, but they are a best friend - you care for them) And in shortening your replies, would you be hoping they'll get the hint you need some space?
Then say, they don't pick up the hint - would you feel even less inclined to text them? Is it possible you (or anyone else in this situation) would think 'she really, really need some space to sort her own feelings out'?
...Is it possible for someone in this situation to feel that their best friend is constantly making them feel uncomfortable, and as a month wears on, and then two months, they start to get more and more irritated with the constant text messaging and feel 'why can't he just wake up and that I need space'?, and, 'Why can't he just realise that I don't want his love?'
And if that person keeps persisting?
Usually that results in driving the other person further and further away, until they feel the need to cut ties altogether.