Complex sentence: Thompson remained close with the Angels for a year, but ultimately the relationship deteriorated when several members of the gang gave him a savage beating or "stomping" over a remark made by Thompson to an Angel named Junkie George, who was beating his wife.
Split into simpler sentences: Thompson remained close with the Angels for a year, but ultimately the relationship waned. It ended for good after several members of the gang gave him a savage beating or "stomping" over a remark made by Thompson to an Angel named Junkie George, who was beating his wife.