In college, there are two types of girls that hang out with fraternities on a regular basis -- groupies vs. sweethearts. They essentially do the same thing, which is becoming besties with these boys, or at least they are guaranteed to be at every fraternity function. These girls are both dedicated, but on completely different levels.
A fraternity sweetheart is the most dedicated of girls (I know this because my Big is a sweetheart). Not only have these girls been hanging around the same fraternity since they entered college, but they practically go through a pledge-ship to become a sweetheart -- which includes learning the history of the fraternity, getting to know each member, baking, cleaning, making banners, etc. She always has an in to their date parties, and always takes one of the brothers to her date parties. A sweetheart is usually from a sorority on campus, in order to strengthen chapter relations, and a majority of the time she's found hanging with the boys rather than her sisters. Sisters of a sweetheart know not to make her pick between her chapter or the boys, because we all know -- most of the time -- she'll pick the boys. This love for the fraternity sometimes seems extreme, but the boys usually love her just as much as she loves them. Sweethearts can always be caught on campus 'repping' their boys letters on t-shirts, wearing their buttons, or standing around their letters proudly. She always talks about the fraternity with a light in her eyes, and a smile on her face. Sweethearts just really love being sweethearts.
Now a groupie is much different -- I myself can be considered a groupie. These girls usually have a favorite fraternity, or maybe a couple of favorites. You'll find groupies at all of the parties, and usually they know a majority of the members. The difference between groupies and sweethearts is the dedication. Groupies don't want to be sweethearts; they just want a good time. The only thing you'll find a groupie making is a cooler for one of the boys, and that's just so she can make sure she secures her date to their next date party. In order to achieve this they bounce between a few favorites, and know a lot less about the fraternity than sweethearts do. Groupies aren't always in Greek life, and a lot of the time they really pride themselves on that. You'll see a groupie in different letters every day, but regardless, she is always supportive of her favorite boys. A lot of the time, she has or has had a relationship with someone in the fraternity, and that's when the love for the fraternity started. Groupies have a mutual unspoken understanding with the sweethearts that we are not there to step on her toes or take her place -- we're just there to have fun. The boys tend to also like the groupies that hang with them (unless you're an obnoxious groupie -- which is totally a thing). The fraternity usually teases us for being "un-loyal" if we're in another fraternity's shirt around them, but overall uses us for PR, and to flirt with potentials, which we don't mind. After all, we do crash all of their functions.
All of this is your basic run down of stereotypes that are true about sweetheart's and groupy's fraternity relations. You always have those rare cases of groupies taking it to the next level, and wanting to become a sweetheart, but you usually know at the beginning of your relationship with the fraternity which one you will be. So, are you a groupie, a sweetheart-to-be, or have you already got your face on their composite?