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.
I'm sorry for the greif you're dealing with right now. Even if it was the issue of distance, she is not handling it well, she is stringing him along like a yo-yo... She needs to make clear she is not into the relationship anymore. Don't mean to sound cold, but it could be the issue that she may want to end it with you, but is afraid to, and is keeping you as a backup incase things do not work out (with whoever she's currently messing around with) you are better than that. Do not be her backup, she's treated you with disrespect. Anyone who is a truly good person would never string someone along like that, especially not someone she claims to love. Believe me, I know all too well about being a backup, my current ex was using me for a backup for a pretty long time til I realized how empty I felt, and that was the reason. he figured he could keep me around just as long as he dropped me some messages here and there and he knew since I was so in love, any little bit from him was enough to tie me over.. I woke up finally and realized it was BS... It hurts just thinking about it, and I'm still upset and in grief over him.. I have no confidence I'll ever fall in love again..
but sorry to go on about me, I really think this girl is a jerk and you need to move on. It will be very hard, but going on this way is no good. You need her out of your system.