A.B.
I think there are some people who live such drama-filled, needy lives, they tend to go through periods where they seem to bond with someone who is fulfilling many needs at once. For instance, you were providing a place to live, saw her through a soured romance, gave her timely advice, helped with her dog. What kind of support or friendship was she providing for you during this time? Probably not a whole lot, though it felt like it because you unloaded on her emotionally. In her own shallow way, I'm sure she cared about you, but the fact of the matter is that you were part of a period of her life, and you are no longer as useful to her. Therefore, she is gone because she needs to pour her energy into the next "bond" that gets her what she needs. That's why she isn't reaching out to you now and why you will always be the one to reach out to her.
My advice: be grateful that she didn't use you worse than she did. Be grateful that you are able to make a clean break. And be careful who you share your private, emotional information with in the future. Know that there are some friendships that are pretty one-sided, and those friendships are almost always short-lived, no matter how intense they are in the moment.