Okay, so to cut a long story short, I have my best girlfriend, Katie, and my best guy friend Jeff. We were all best friends in high school, but they met in 2nd grade.
Jeff and I started to like each other in 10th grade and tried to date throughout high school, but things did not work out because his parents would not allow him to have girls over or date them, plus they were from a different country so they had stricter ideals.
My friends did not like how he didn't make any effort in high school and Katie hated the fact that everything unintentionally got put on her (like our problems) and always was mad at me. After 3 years of trying to date, I broke up with him in August. But it was one of the hardest things I ever had to do because I was in love with him, I didn't realize it was the same.
I finally get to college and the transition has been rough. Katie keeps guilting me because I didn't go to the same college as her, got mad when I mentioned his name one time AND she finally told me, after hiding it for 3 years the reason she always got so mad about Jeff and I. She used to like him! I was insulted that she didn't tell me.
Additionally, Jeff came to the University to visit me the second day I was here--I assumed it was just a visit. Nope, he came to beg for my forgiveness and ask for me back. Although it didn't work out that way. So he came up with this really lame hypothetical situation to tell him that "This guy really likes this girl and they dated and broke up because he knows he screwed up, now he's afraid that she's moved on and he doesn't know if he should do anything about it or just leave her alone."
Now we have been visiting each others' colleges almost every weekend an any chance we can get. Katie doesn't know about this, but I know she would be pissed. She never told me though, and I think she still has a clue that I still have some kind of feelings for him even though I told her I'm over him a long time ago.
I need to talk to her about it because Jeff and I really want to have a true relationship this time, but I don't want to make Katie mad or have her completely disown me as her best friend. I'm scared because I don't want to lose her or him. They both mean so much to me... and despite all the crap he put me through in high school, he's really taken a 360 degree turnaround. He makes me really happy, but I don't want to lose my best friend Katie...

Please help. I described my situation really badly, but that's the best way I could do it, so if anyone needs clarification, I'll be glad to provide it.

Just tell Katie straight out. Sure she's your friend, but you don't owe her any explanation.

I can't see why she would still get mad at you for dating a guy that she had a crush on years ago. That's just plain childish.

Seriously, so what if she gets ticked off? She'll get over it!