Having kind of a problem here. My girlfriend has a really good friend who happens to be a guy, He's actually the guy who kind of set us up. However, lately, she's been kind of cold to me, and she's been spending an awful lot of time around him, even while I'm around.This is unsettling, since we just hooked up, so I'm not sure if she said yes just to humor me.He told me he doesn't like her, but now I really am not sure. Now I even hate him. Please help.

Ask her.
If she's straight with you now and tells you she's done with you, then you can get this off your chest.
If she lies and they're together behind your back, you can forget her.
If he wants her but she doesn't return the sentiment, at least you know what's going on.
If it's all just a misunderstanding then you can relax!

yeah, there's two options:

Ask her - result: she is, or she isn't. You can probably tell if she's lying or not.

Don't ask her - result: you spend a lot of time worrying, never knowing, and try covert ways of finding out.

Trust me, I know it will be awkward, but it's got to be done.

Just be direct.

Very sorry. No one is immune from this. By the way, now there are many who will help solve the problem and set everything up in places before. https://infidelityprivateinvestigators.com.au/contact/private-investigators-adelaide/ I followed my ex when I suspected her of some things.