Complex sentence: Tired of pretending to be Mitch, Dave has them go back to his house to tell Jamie the truth, but Jamie does not believe them due to Mitch being the only one of the two that knows their anniversary date and Jamie's favorite color.
Split into simpler sentences: Tired of pretending to be Mitch, Dave has them go back to his house to tell Jamie the truth. However, Jamie does not believe them due to Mitch being the only one of the two that knows their anniversary date and Jamie's favorite color.