Dating My Teacher's Brother

During a rugby match, Rachel Hicks' teacher Mr Paul Williams, introduces her to his younger brother. Rachel has always went to her brother's rugby matches and Sean Williams always caught her attention. After exchanging numbers, the two go on dates and Sean transfers to Rachel's school. The couple become closer than ever before and spend most of their time together. But since they went public with their relationship, Rachel has witnessed a difference in Mr Williams behaviour towards her. As the couple become closer and closer, she feels more awkward around her teacher.
What is wrong with Mr Williams?
And why do some of the teachers take interest in their relationship?
Can dating a teachers brother really be that stressful?