So my girlfriend is Mexican and naturally speaks Spanish and so I see her get this message from a guy who she says is her best friend which reads "aha te quiero :* :*" I don't know Spanish very well but is this something I should be concerned about or is it cool?
It means "I love you" but I'm almost sure he doesn't mean it the way you think. When we say it in the romantic way, it's usually "Te amo" what you are looking for, and even then it can be just an expression of affection from a friend (specially if she just helped him with something).
You also have to take in account cultural differences. Latin people usually express our feelings in a way that other cultures may see as exaggerated, and there are also differences among countries. I'm Spanish, and over here, a "te quiero" it's nothing really that serious, specially after an "haha", but wait until someone from mexico confirms it the same over there.
In spanish "Te amo" is too strong, so if you want to say that you have good fellings on someone but not necesary love, you say "querer". "Te quiero" means "I like you" most of the times. You can say it as "I love you" but the context makes clear wich one is the correct one. Here he's only saying "lol luv u" or something like that haha.