Complex sentence: In 1968 he moved to Paris where he met Alain Boublil, with whom he wrote the libretto for the musical Les Misérables, since he has written for many artists and recently some of his poems were set to music by Franck Pourcel.
Split into simpler sentences: In 1968 he moved to Paris where he met Alain Boublil, with whom he wrote the libretto for the musical Les Misérables. He has since written for many artists and recently some of his poems were set to music by Franck Pourcel.