Should I tell my boyfriend I need a break from our relationship in order to find closure with my ex?

Of course you should. He doesn't deserve to be strung along while you figure out your feelings for another guy! Let him go.....

If you are not that in to him and still hung up on you ex, then it would be fair to tell him. However, in the interim you don't get to say that he cannot find a woman who likes him as much as he likes her.

Yes. Why did you even start another relationship when you hadn't recovered from the one before? That is a selfish thing to do.