Most Helpful Guy
No. Rebounds are typically bullshit and he's actually using this poor girl to bury his grief. You need to give yourself time and space after a breakup.
Otherwise you take yourself with you to the next relationship without looking into what went wrong and spending time doing a bit of self evaluation.
He may act all happy and think she's great, but if he had any ounce of feelings for you, he's not doing anything but running from one relationship to another and using whomever he's with.
Most Helpful Girl
Just let whatever is going to happen in your relationship happen. I know it's hard but I'm going through something very similar. We can't change our men, they need to change for us. If he is this quick to be with someone else, he may be using this new relationship to distract himself from what's he's feeling, maybe to make you jealous, maybe he just doesn't care. In any case, you need to let what's going to happen happen and find you a man who you deserve. Don't let anyone tell you otherwise.