Should I trust her?

My girlfriend of about a year keeps in contact with a guy she claims "used" to like. I'm not so sure if I should believe her or not.

She's the jealous type (as am I) and has made me break off contact with any and all females that I had any kind of relationship with. I've pushed for the same thing with her friend (we'll call him Karl), telling her I don't like it that she and Karl text, etc. She claims that now he "repulses" her and she has absolutely no interest in him and continues to talk to him, despite all protests on my part.

Earlier this evening, we had been out drinking with some friends, and as usual, she started texting Karl. Now, she's the snoopy type. Going through my phone to see who I text, constantly checking who I'm talking to on Facebook/Myspace and all that. She is VERY protective of her phone and will never let me look at it to see who and what she's texting. Anyways, I get mad because she's texting him and we get in a little argument that she's not just texting him but Karl's ex (whom she had been friends with and recently started talking to again) also.

She said she wanted to go hang out with Karl's ex (her old friend) and we leave the party, go home, get directions, and drive to her friend's place (we'll call her Samantha). On the way to Samantha's, her story seems to go awry. Saying "I think this is Amanda's house. I haven't been over here in a long time." When we get there, I start to pull in the driveway and she freaks out telling me to just pull over and drop her off (I have to work the next morning). She tells me she loves me and gets out and leaves.

As I'm pulling away, a voice in the back of my head say "You don't know for sure this is Samantha or Amanda's place, this could be Karl's." I call her up, to make sure it was the right place, which she promptly sends it to voice mail manually. I text her asking if it was the right place, etc, saying if she needs me to come pick her up to just call. When I get home I look up the owners of the house using the address she gave me to look up directions. Lo and behold, the house I just dropped her off at is none other than Karl's parents' place. I immediately call, she won't pick up. I text her demanding to pick it up. She finally answers and I confront her demanding to know why she lied to me and had me drop her off at Karl's place and tell me it was one of her friends' places. She denies that it isn't his place and it's really her friend's place over and over.

Very mad I drive back there and park, texting her to come outside and to bring Karl with her. She texts back saying "i'm only with you don't be worried you are my only" I go to the door and ring the doorbell (at about 3 AM, mind) and she starts texting me, telling me to go away, that I'm scaring people, that she's fine, and that she'll be home tomorrow.

She demands I trust her and then this happens. I really don't know what to think. I've been up all night worrying and I feel betrayed to all hell. Please help.
Should I trust her?
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