I think you were totally in the right. Something similar happened to me with my girl.
We had been dating for about 2 1/2 years. We had a few rough patches in there, but we hung with it. We both enjoyed each others company and couldn't stay mad for long. That's the back story.
She plays World of Warcraft religiously. I'm the one who turned her onto it, but I quit playing. It's mostly guys that play, but I'm a trusting guy. She had never given me a reason to not trust her before.
Comments from guys I didn't know started showing up on her myspace page, myspace is the devil BTW. I keep a page just to have one now, hardly ever check it. Didn't bother me, girls that I barely know leave me comments on my page. However I noticed alot of comments from this one guy that lived out of state. I asked her who he was. She said it was some guy in her guild on WoW. That was cool, I'm not against her making new friends.
Wow this is getting long. Long story short: She was planning a trip to meet him. He offered to fly her out to his house so she could "apperntice" or some bullshit. I found out by reading her messages on myspace. Several things happened to make me suspicious enough to go through her messages or I never would have. Did I mention he was like 20 yrs older than her?
I broke up with her, we got back together. It's been about a year now. She still plays WoW. I set some hard rules that if she ever violates I will leave her over. I felt it had to be done for the time being if she wanted back in my life. I know longer tolerate any shape form or fashion of any bullshit. I don't know if I'll ever fully trust her again. We probably won't take it further than dating.
Back to you, you were totally right in doing what you did. You can't waste your life on girls that just bullshit around like that. You can find someone a lot better than the one you posted about. Women are everywhere.
Sorry, I ramble when I'm stoned.