I have zero experiene long lining. I'd love to have a lesson from a knowledgeable person on this wonderful skill.
but, what's more important, just not being able to lunge him is the more fundamental issue. just learning how to 'send' your horse away from you comes first, and that is built on being able to move his shoulder over.
one you can make him yield his shoulder sideways, away from you, you can make him move out on the circle. then, with a lunge whip, you should be able to make him go forward. if you can't make him go forward, then I'd back down to a round pen and just MAKING him move good and fast around the pen, just to establish your ability to move his feet.
then, you get so you can move his shoulder out, so you are able to make him move around you in a circle. don't start this with a whole long lunge line, it's too much to control. use about 12 feet of line, instead of 22 feet.
most people will try to make the horse that insists on facing them go around a cirle by trying to walk around where they are at the hroses hind end to drive it forward. but, the smart horse only turns on his front legs to keep his face toward the human, so the human ends up moving more than the horse. sound familiar?
you need horse to step off to the side. so, make him move his nose, then his neck , then his shoulders over to the side, away from you. do it by walking straight toward the hrose, with you hands ready to tap him sharply on the nose in a way that 'pushes' him over to the other side. if you keep walking and tapping on his nose, he will move it so far over to away to the side, that he will HAVE to move his shoulders, too. when he does, you stop pressuring him. that's his reward.
rinse and repeat. pretty soon, you just sort of 'air tap" toward his nose and he'll move away, then you get to where you can just point, and he'll move away.
once he has stepped his shoulder over. you hold your leading hand out in the direction you want him to go (he's now more or less facing that way), and you use the whip behind his hind end to ask for forward movement. voila! you are lunging.