it's really a simple fix. if you can't decide on this matter, be single. that way this all blows over. no one else put you in this situation except yourself, so only u can fix it. also, this is a big sign that you really don't know what you want in a relationship if you're feelings are always darting from one person to the other. Also, honeslty, i don't really think you're ready to commit to someone. nothing wrong with dating around if anyting, just don't get INTIMATE with them. good luck either way, it's your call.
I was at the Sheffield show! It was awesome :] + I don't know about Sam and Josh I think I'd leave it a week and see how you feel after then, If you still have feelings for Josh after then is it really fair on Sam to stay with him?