One thing I would like to say is when your lunging your horse make your shoulders a wall towards his barrel, level with his shoulders & hip. Stay still, in the middle..
If any horse threatens you, threaten them back!
When your horse came around you.... You gave him a open invitation to come into your space, if that happens step at him, arms up & scream YO!!! & check his ass right back out in that circle!!
I would definitely try to start making his lounging a bit more mentally fun for him.
Try working all different transitions (walk, trot, canter, stop backing, turning) faster, slower. The more you make his feet move the more attention he has on you!!
When you start lounging, send him right off in that circle, dont give him a moment to think about anything but you! even when his head pulls your arm away, give him a tug back & send him off in a different direction, or make him change transitions. Make him think about distracting away from you again! or make him work for it.
&&&& for the girth!!!!
Start off slowly, like one little hole at a time if you have to, everything is baby steps! if you can put a saddle on his back & take the girth around his belly and he is fine about all that but the moment you zip up that girth he brings his head around to nip you, you maybe doing it to fast and tight.
Bring the girth up super slowly slowly & softly to see where he starts bending his ear towards you or OR JUST BEFORE that moment when you know he turns in to nip, EVEN going slow and soft just STOP & clip it there. walk away. He will be SOO confused!!! If he was tense he will drop it & be left thinking.
See you have the power to give and take pressure.
USE IT AGAINST HIM!
If you know the second before he will do something, leave it just right there & step away, he will take a breath and be relieved.
After he stands for a minute return, pet him & start just handling and fondling the girth, dont bring it up just play with it & wiggle it.
because here your not tightening it your just testing the waters & his attitude.
If he turns & bends in a inch to nip crack him one before he even know what hit him!
After that, try to bring up your girth, again softly and slowly up the next hole or two. If that doesnt work I would put him on the lounge line & if he tride to nip again I would back him to the moon every nippin chance he tried to get!
Your working baby steps & testing his boundaries & catching him before he can react...
He sounds like a sneaky little boy & you may just have to get one step a head.
A Lot of horse language is needed
"If you have control of the hoof you move the mind."