Just tell him that you are sorry that that just happened to him, but that he will ultimately be better off without her, because she wasn’t a good match and she just doesn’t feel the same way about him. That’s all. Tell him that you think he’s pretty cool and good looking and nice, but that his ex just wasn’t the right person for him. Then ask him if there’s anything you can do to help him get over her (I’m assuming that you don’t have a crush on him do you?).
The other girl probably didn’t mean to hurt him, but people, especially young people, although they clearly can and do feel love and passion, just like older people, they are often unsure of what they really want and need in a mate, because they haven’t had enough experience with enough people to have it all figured out. So at one time they think they love/want one particular person and them poof! a few weeks later they feel differently (and they have no idea why they feel differently).
Also let him know that younger people, who have not yet learned more mature communication skills, often say things that they don’t exactly mean, or they put things in a way that will hopefully let the other person down more easily. Unfortunately, that doesn’t always work. So his ex girlfriend, who probably really did love him at one point, probably fell out of love with him for reasons that no one (not even she) can ever understand (some biological, some hormonal and some completely unknown factors). But because she didn’t want to hurt his feelings, because she probably did and still does care for him, she told him that her parents wouldn’t let her have a boyfriend (which may have been true, but may not be true currently true for a whole host of reasons).
It’s too bad that the ex girlfriend wasn’t mature enough to be able to tell your friend that she fell out of love with him. I can understand why, though. Because she probably still cares for him, but not in that way. It’s pretty brutal to have to tell someone that you don’t love them anymore. A lot of people lack the maturity to be able to be honest with someone without hurting their feelings or humiliating them, so instead, they say nothing and then hope that the other person will figure it out or get the hint. But people aren’t mind readers so that usually doesn’t work, and someone’s feelings ultimately do get hurt, but much further down the line.
Let him know too, that if he doesn’t want to talk to the ex-girlfriend about the new guy that she likes (which would be pretty painful for almost anyone) that he should gently let the ex know that it hurts him and makes him un-comfortable because he thought that she and he were going to get back together. He doesn’t need to be mean to the ex, either, but he should just let her know that he needs to let her move on with her life, without him, otherwise he’d feel like the third wheel. Nobody should have to put up with that.
And you, as a good friend, should just be supportive and never make any unkind remarks about the ex girlfriend. Just keep reminding him that he’s terrific and that his relationship with the ex just didn’t work out, that’s all. Now he’s free to find someone else that he likes, even better.
If he’s not too shy, have him come onto Fluther! : )