How to stop relying on her for happiness?

I think you both need some time away from each other. There is more to life that just family even though you are very close. She is probably experiencing the joys of exploring new friendships. In time, every life takes a turn and the sooner you accept it mentally, the better it will be to adjust when it does happen. For the short term, I would suggest that you accept this normally and do not try to lay a guilt-trip on her and see what happens. When she needs/misses you, I believe she will come to you for advice. I think this is just symptomatic of growing up. Hope this helps!