I think he was angry with Liam. Brian REALLY likes Amanda and although she continues to be charming, her body language totally shows that she does not fancy Brian. She is also TOO nice and is afraid to be honest with him- maybe she thinks it will affect her chances of winning, or maybe she is just too immature to know how to let someone down gently. She has said already to others that she does not fancy Brian. He is coming on too strong- like an octopus. He is alwyas there, always touching her. She politely declines. They snogged once when drunk so he thinks now that she likes him. So, when he sees her being all tactile with Liam, it upsets him. I think he knows he is onto a loser here.