What Allie said is really true..
Anyway try to think for a few seconds this: If you two ended it, and she got another boyfriend, how would you feel?..
And about the happy tears. A lot of my friends went through what you did, honestly I didn't but I kind of understood what those happy tears were. Most of the time, they are relieving tears.. I mean, from what I understood you had that thought that she had some1 else in her heart, so you already had those sad tears deep inside, but then when you went through her FB page, and got to that conclusion, you probably were relieved from that thought thinking you finally found out the truth.. Better not end it yet, because just from questioning that you truly love her, means that you are scared of not loving her. In other words, I can't say this for sure because I don't know you, but I'd say you actually love her.
I hope this helped, even for a bit.