Advice request...

She knows I have other girlfriends, she knows I have a boyfriend as well. She knew that before we got together and it was ok with her.
FYI, I'm a girl.... so naturally I'm not 'boyfriend material'.
And had that been the case, she shouldn't have been telling me 'oh, its ok you're sick, I still want to come over, I missed you this week. You know I love seeing you either way'. And she should have just said 'hey, I'm going to hang out with J tonight after we finish D&D, I'll see you tomorrow'. That wouldn't have bothered me. As long as I'm told where she is going(in case her parents call me and ask) and am given notice I'm fine with it. She knew that, I told her that last time she did this.
And as for the money, it has become an issue. Its getting to the point where it feels like I'm being used. She comes over, eats my food, leaves, comes back, eats more food, and I drive her home. All this for nothing in return. Feels a little one-sided.
 
Its difficult to give advise when we don't know you Serenity. Sometimes its best to speak to your best friend or other close friends. I think in this case, you just needed to blow off steam.....I will offer my comments in red within your original post.

So early yesterday I got quite sick, and had to go home.
I understand you work as an SP in the Kitchener/Waterloo area for an agency (ASA). I take it you left early due to sickness.

One of my girls had been planning to come see me.

Same comments as Hunter, you call her one of your girls. When I first read this I thought you were referring to one of your daughters. It sounds controlling, does the girl know you think of her as one of your girls. In a more recent post you note that while she is in the city with me her parents have left her under my care and responsibility. They expect that she will be with me, at my apartment, because that is where she and I told them she would be. Just how old is she. How would her parent react if they knew you were interested in sleeping with their daughter (not that there's anything wrong with that).

Knowing I was sick, she still wanted to come and hang out.

Even though you were sick, you tell us you drove for an hour to pick her up and then drove another hour back to your place so that you and one of your girls could hang out and play games.

We've done this a couple times before, she comes over, stays the night, then we drive her home the next day.

On fridays we have friends over to hang out and play games.

Are we talking euchre, crazy eights or some sexy version of spin the bottle. Ya, I'm a guy and this does interest me but if a bunch of you are getting together to play trivial pursuit its a little different than playing let's hid the kabossa. You mention that she left to play games at someone else's house, so I assume we're talking sexual games.

Last night I went into the kitchen to put my glass in the sink while everyone was packing up to leave. I come back in and my girl has her coat on. She informs me she is leaving with one of them, and will be back sometime the next day(today). No warning, nothing. She still isn't back either.
Normally this kind of thing would bother me, except I had no warning, and she was supposed to be there to see me, not the other person. On top of that, it was the second time she has done this, and I talked to her about it last time. She lives an hour away, so the gas to drive her home, and get back home myself after isn't exactly cheap. We also feed her while she is here. And she doesn't pay me back for any of this.
I've been majorly pissed off since the only reason I don't ask her to pay me back for everything is I want to see her too, and then she leaves to go hang with someone else for the night.
Am I overreacting? Or should I just tell her if she wants to come again, she can find her own way back?

Are you overreacting, I'd say yes, but that's human. Please do not take this the wrong way, but since you are Serenity_ASA, (from what I hear, a very beautiful and fun to be with SP, it may be better to not place this type of post on the board under your professional name. Create another identity letting the masses know that you're an escort in the GTA. This particular post under your known name and associated with ASA is not a good idea. Contact the Mods ask them to pull the plug. I'm not saying hold everything in, write down your thoughts, sleep on them and post away but under an assumed name if necessary.....
 
FYI, I'm a girl.... so naturally I'm not 'boyfriend material'.
Well it might have been good info to post up front. There isn't a way to tell from this side of the screen.

If money has become an issue ask her to bring food, and take a bus to town and you will pick her up at the bus station, or ask for gas money. There is no shame in asking.

As for her leaving the get-together with some one from your place I don't really see the issue if she wants to hang out with some one she likes. I get it is kind of rude to leave with saying "bye" . From her point of view it she almost like she has to ask permission to leave.
 
And as for the money, it has become an issue. Its getting to the point where it feels like I'm being used. She comes over, eats my food, leaves, comes back, eats more food, and I drive her home. All this for nothing in return. Feels a little one-sided.

There's a saying... "no one can take advantage of you without your permission."

If you feel that your friend is trying to take advantage of you... then stop letting her come over, stop feeding her and stop driving her around.

You've said that her parents are expecting you to look after her... how old is she?

And if you have agreed to this arrangement with her parents then you should have called and told them when she took off to somewhere else IMO.