Once you let a horse get away a time or two, they have won a BIG battle and they know it. He is now truly spoiled for longeing. Get a chain over his nose or bit him up or both. MAKE him have form. Get control of what his head is doing and you will get control of his actions.
I have had horses brought to me that bolted 100% of the time if a person gave them more than 4 or 5 feet on a lead-rope. I had one 1200#+ mare that was brought to me that had rope-burned the hands of everyone that had tried to lead her. I had a 'snubbing post' in a big square corral where I handled un-halter-trained older horses that were brought to me. I longer her in that pen with the longe rope dallied around that post. The post was the only thing that could hold the big pig. Once I got her longeing around that post, I taught her to work bitted up and then started longeing outside bitted up.