How to tell my boyfriend I don't like his hair?

I've been with my boyfriend a year and a half and I absolutely adore him, he's everything I could ever ask for. When I first met him, he had shorter, cleaner-cut hair and I thought it was cute. He's never been one to dress that nicely either, but that's something I totally accept because I love him despite the fact that I love fashion. But his hair is out of control. I'm not sure why he let it get like this, but it looks a lot like the picture attached (same color and everything) except much more scraggly and trashy looking. I love him so much so I've tried to restrain myself from saying anything because I care more about what he's like on the inside (clichè, I know, but true), but he would honestly look so handsome with short hair. I mentioned it once and he said his forehead is too big (it's not). Help??