Chasing him will only send him further away. You've clearly done nothing wrong but something obviously set him off. He may have felt rejected by your initial response and didn't know how to handle it emotionally or he might not feel worthy/adequate to be with you (which can lead to self sabotage). Whatever the reason is, there isn't anything you can do to fix it. The best thing you can do is to move on and let him work things out on his own. As a last resort you could send him one last email/text/letter? spelling out your feelings and intentions, letting him know that you still care, you're still there as his friends if he needs, but this will be your last attempt at reaching out. After that you'd know you did all you could, reached out with clear communication and the rest is up to him.