Complex sentence: Lane had seen Mariani in the final few gigs of the Go-Starts and asked him for guitar lessons which became jams, then writing songs, and finally the decision was made to form The Stems.
Split into simpler sentences: Lane had seen Mariani in the final few gigs of the Go-Starts and had asked him for guitar lessons which developed into jams, and then writing songs. Finally, the decision was made to form The Stems.