Complex sentence: The same episode revealed that Martin moved him in order to avoid expelling him, which would have upset his new girlfriend-Grayson' mother, meaning that Alfie and Grayson could become step-brothers if they married.
Split into simpler sentences: The same episode reveals that Martin moved him in order to avoid expelling him, which would've upset his new girlfriend. The woman is Grayson's mother, meaning that Alfie and Grayson could become step-brothers if they married.