Help with my standardbred jumping?

i have a 15.1hh 9 yo standardbred gelding, he was late broken in (when he was 6) as i bought him off my uncle. Up until about 15 months ago he had progressed so much (schooling was fab & was jumping 1.30m). As i was busy with school work etc i my friend who had my 14.2hh showjump pony on loan was riding him for me (i was always there to watch her ride him) we didn't realise he completely changed shaped & as his saddle is a made to measure saddle it didn't fit. I broke my collarbone (after him taking off with me & getting flung into his stable door) & couldn't ride for a while so as i wasn't riding him we got him re-measured & saddle sorted, when i took him back into work it all went down hill from there. He was ridden on a snaffle & now has to be ridden on a pelham (i have very light hands) but as it severe he throws his head up & paces, but any less severe bit he rears & bolts (we have had him checked in every way possible and he's fine). He is finally starting to respond nicely in the arena if i warm him up on a hack first (he is great hacking) but when we jump he either gallops to the jump/pole & stops on landing, or paces to the jump/pole & turns tightly & stops, i have put other people on him to see if it is my riding but he wont even trot without throwing people into fences etc, i just want him to be back to normal and i couldn't dare part with him because he has been in the family since he was born. On the ground & hacking he is an angel.