so, even when you are inthe round pen and hook a lunge line on the halter, he will not go around? He only turns in and expects to be lead. I think that he thinks he is being a good horse. "when she puts a lead line on me, I should wait to follow her" Sounds like he is a polite fellow.
You may need to get him to understand what lunging on a line means, and you can have another person help you with this by actually walking him foreward while you stand in the middle, and YES , get and use a lunge whip. not like a whip to strike him but as an extension of your arm so that you can put a bit of pressure on him while you are far away .
YOu may have to add a bit more pressure initially to get him to understand.
When a horse won't lunge it is almost always that the handler doesn't realize that the horse is correctly reading their body language; the handler isn't saying with their body what they think they are saying.