A new horse
You have had him only for a few days - take it easy. He is in new surroundings. He has lost his mates and you are a new rider to him.
To settle him down will take time. He has got to get to know you.
He is the right age and by the sound of what the young lad did, he knows what to do. He has just got to learn to do it with you.
It is all about confidence, yours in him, his in you.
Go back to basics. Walk and trot and slow canter only when you are ready. Same route every time for a bit. Let him build up a map of the surroundings. Get to know the feel of him.
The idea of tuition is a good one - someone knowledgable needs to watch the pair of you and see what's going on. It would be a good investment.
If you give him a bit of love that's good - he'll know. But if you are nervous, then he'll know that too.
Take it easy.
PS Ask your riding partner to take it a bit easy next time.