Hollywood couple Heath Ledger and Michelle Williams' relationship is in trouble because film commitments are driving them apart, according to reports. The couple have been engaged since 2004, after they met on the set of Brokeback Mountain, and they have a 23 month old daughter, Matilda. But friends say their busy schedules mean they are barely together. A source tells British newspaper the Mail on Sunday, "Things are not looking good. They have been filming in different locations and it has put pressure on their relationship. Heath especially exhausted and under a lot of stress."