Ok, so it's time you had a talk. Start it off with a comment to the effect that you should have done this earlier, but it's better late than never.
However before you talk with her, I just want to touch on some of the other issues you mentioned.
- put on another guys t-shirt after we had sex as her pajamas. It was in her overnight bag she brought to my place. I made a comment about it being big and she said it wasnt hers. I let it go. She puts it on again a week or so later at her place and I make it clear not to wear it.
I don't have a sentimental bone in my body, so I can't see the issue in her wearing another guy's old tshirt. Back when he was my boyfriend, my hubby wore and used items which were gifts from exes and I don't see much difference. It's a non-issue. In the case of your girlfriend, the shirt probably just got left at her place and was comfortable to sleep in so she sleeps in it. I would, however, be concerned if a boyfriend dictated what I can and cannot wear. I would have told you to pull your head in.
-My shady acquaintance that introduced us always hits on her and mid October while we are out, he asked for her number and she gave it to him
That was back in October - BEFORE there would have been any expectation of exclusivity. Let it go.
-We are out with the same shady guy for NYE and he and his date take a picture. Then she asks the girl to take a picture of her "with my two favorite boys". No picture with just me. That pissed me off
You're making a mountain out of a molehill. If you want a picture with you and your date, just say "hey, I want one of the two of us". You're placing secret expectations on her and getting upset when she doesn't meet them. And this was certainly not worth getting pissed off about.
Go and talk with her. Find out what she wants from a relationship. But stop making assumptions like she's been having booty calls in the last month and finding problems where none exist.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.