OK, I will try my best to help you with this one. However, please keep in mind that I'm not an extremely good writer, OK? lol
1. What was your friend's problem? What king of huge responsibility did you have to take? What was actually going on? I know that those matters are quite private, but try to clarify the situation at least a bit. I was kinda confused while reading your essay.
2. You start with present tense and then switch back to past tense. I suggest you chose one or the other. In this case, probably past would work just fine.
Those were 2 big ones; time for some details:
irritable, loss of interest in everything, weight gain, and recurring feelings of hopelessness
All of those should be parallel, which means if you started with and adjective (irritable) then stick to the adjectives. Here, I would suggest using nouns. Maybe try: "irritation, loss of interest, weight gain, and feelings of hopelessness" ?
As the signs began to manifest, so-called friends began distancing themselves. Maybe they didn't understand the depth of the situation, but it was evident they didn't want to deal with her.
"They" in the 2nd sentence refer to "so-called friends". OK. But whose friends were those "so-called friends"? You can write: "Kelly's so-called friends began distancing themselves from her." and it all becomes clearer.
I was no longer afraid and unsure.
What made you change your attitude? Elaborate.
Those are only a few things I could think of right now. If I come up with any other ideas/suggestions, I will let you know.
GOOD LUCK WITH THE APPLICATION! ;)
Oh, and here is the link to an AMAZING, in my opinion, essay (also to Villanova). :P