Why do I just care about her happiness more than mine?

Okay so a little background information: My friend went out with a girl for like 3 months or so. During this time I became very close with who he was going out, and we became good friends. I became her outlet for relationship problems, and I was kind of "in the relationship" it seemed because at one time I was on Facebook and BOTH of them were coming to me about what they should do. I kind of freaked out and let them know that I didn't direct their relationship. I shouldn't of freaked out, but it was just getting ridiculous! Anyways, we were all cool, because my freak out wasn't that bad. I just let them know. But I digress... I became her relationship advisor, which was cool because I had every chance to stand up for my friend. It got to the point where I knew that she was unhappy in her relationship a MONTH before she broke up with him. When she actually broke up with him I was at a water park and I left my phone in the room. When I got back I had a text from him, a text from another one of my friends, and a missed call from her. I excused myself to go in the hall so I could call her back. When she picked up it seemed like she was almost in tears, she had explained that her friends had pressured her into doing it. I comforted her, all the while I was confused. In the weeks that followed she relapsed and realized that she still loved him, and talked with him to explain that she just wanted a break. However, he moved on, while she still got teary eyed thinking about him. Throughout their relationship on my part I started realizing that I had feelings for her, do to the fact that we talked a ton and had a ton in common. She didn't feel the same, but she did say that my conversations with her were a lot more exciting than her conversations with my friend. Recently near the end of school we went on a grade wide trip to a water park. Both of her friends had guys they were hanging out with and she felt like she was a third wheel. That was the first half of her day, my first half was hanging out with my friends nonstop. However me and my friends moved to the indoor part where she was with her friends. It turns out my friends ditched me, her friends ditched her, and one of my friends was also there. So we formed a three person group and we hung out a lot for the next 2 hours. She constantly talked with me about wanting to have a boyfriend and how lonely she was. Before her friends actually ditched her we were all in the lazy river and she was talking with her friend about how she wanted to have a boyfriend. Her friend suggested she went out with me (I don't know if it was sarcastic or not, but it sure seemed like it was) and me and her met eyes for a second, and then she jumped to saying "No!" and she came up with some of the worst excuses possible. It was actually kind of funny. But I digress again, whenever she went to me for advice I pointed out other people. I feel like I wouldn't be able to make her happy, so I ignore my feelings for her happiness. I talked with my friend (the one who went out with her, he's the only one who knows about my feelings for her) on the bus ride home and he criticized my lack of doing anything about my feelings for her that day, and he even told me that I wouldn't get a better chance. But I realized I didn't want my own happiness, I wanted her to be happy. Why is this? If you actually read through that, thanks! :D