You have something he or she wants.
Ever offered to help with something? Isn’t it funny how someone will swoon for you, sweet talk you and make you feel like the only person in his or her world until he or she gets what he or she wanted?
You helped this person in one way or another, so now, the person doesn’t have to try so hard.
He or she will step back and push you away a little bit because he or she doesn’t really need anything from you anymore.
You played your part, so now you have to go. Or maybe, he or she doesn’t really want you to go for good, but you are no longer a top priority. You will know when that happens. Timing is everything.