Bless your heart...I am sorry.
For clarification, at what point did you lose Tim? I understand that you regretted it (and I don't like the fact he pressured you into something you weren't ready for...I'll get to that later), but did that cause you to break up?
If that's the case, I'm not sure you have much to feel bad for. He pressured you to do something you weren't ready for, and you have a right to feel bad about that. HE should feel bad for pressuring you, as I see it, but that's me...part of me can't help but wonder if he exploited you and your emotional state after breaking up with Luke for his own gain, which I neither respect nor approve of.

I don't know enough to make certain that judgement based on what I have though...it's only merely my suspicions, and my general disapproval of anyone "pressuring" anyone to do something they don't want to do themselves.
If you wanted Tim back, if it were me, I'd sit him down, explain how you felt and why, etc etc. It would be better to lay it all out and explain why you felt that way than to try and skirt around it, but that's me.
I hope I was of some help. Please don't hate yourself over this.