Give it the Summer, express your interest once you return. This will give you guys space to truly realise what you want and need. Fair enough, I understand that there is nothing exactly wrong in telling her now except that I think it's rather selfish and unfair on your part, she has only just started dating new dude, if she still has feelings for you then she will be easily swayed because they are naturally greater than what she feels for him, poor new dude doesn't stand a chance. But do you want her to pick you just because you happen to be the easier choice?
Who knows what will happen over Summer - maybe subconsciously you only want her back now due to the fact that she's unavailable. Time will confirm whether this is true or false. Also, her relationship may fizzle out over Summer or she may figure out that her feelings for the new guy on the scene don't run deep and that he will never compare to you - either way, you should give her the opportunity to realise this for herself. If you initiate reconcilliation now and your relationship deteriorates once again, she will resent you for it, that she could well have had the chance for happiness with the other bloke had you not intervened.
[SIGPIC][/SIGPIC]
Love is like a merry-go-round: you get all dizzy, and then you feel sick!