Complex sentence: However, when Laurie begins buying Kathy extravagant clothing and jewellery, she questions his motives, thinking he's trying to make her look like his late wife, and loses interest.
Split into simpler sentences: However, when Laurie begins buying Kathy extravagant clothing and jewellery, she begins questioning his motives. She thinks he is trying to make her look like his late wife and loses interest.