Dude, before i say anything, sorry if i may sound harsh.
What were u thinking when u met B and started realize u felt more n more comfortable and closer to B...did u for once think or remember A is ur GF???!
Given what has happened and all, u did not even have the courtesey to tell A the truth!
You are more concern of who to be with or not to be with???
Shame on u ...
What u should do is, to explain everything A to Z to both A & B (B knows everything already right?) and let them decide if they want to be with u ... I dont think u have any rights to decide after what u have done! The complication will be if both A & B decide to be with u after knowing what sort of jerk u were..the bright side is, which ever accepts u despite of what u have done...i shud say..u are one of the lucky guys around to be forgiven and loved by her...her act of forgiveness and acceptance will make u sure n clear u are with the right one ( BUT doesnt mean u can go falling in love with a C D E F or Z!!!)
Hope my words gives u some wisdom and understand what to do next =)
ANyhow, Good Luck n post wat happens next mate!
+100 for you. I also think that TS only think of himself. To girl A and girl B, please dump this guy and find a better one.