Sorry you're in this position. Unfortunately, this isn't about why he is ignoring you - it's about why the whole group is ignoring you. Something has happened to annoy them or upset them. Have any of them given you any clues as to what may have gone wrong? If not, it's very immature of them to exclude you in this way.
You're new at this school yes? My best advice is to leave this group and find some nicer friends.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.