Complex sentence: He formed the Allen Collins Band in 1983 from the remnants of the Rossington-Collins Band, releasing one tepidly-received album, but many around him believed that the guitarist's heart just wasn't in it anymore.
Split into simpler sentences: He formed the Allen Collins Band in 1983 from the remnants of the Rossington-Collins Band, and released one tepidly-received album. But many around him believed that the guitarist's heart just was not in it anymore.