There are several themes in A Look Back in Anger, but I think the most obvious is class/social structures of society and how the terms that come along with them affect people and their everyday lives. Jimmy and Alison are, at first, probably pulled together by some attraction towards each other, but only to have it solidified because Jimmy envies where Alison comes from and she being upper/middle class tries to rebel against that by marrying someone "beneath" her own social class. Her parents are not pleased by Alison's choice of husband, again going back to the class theme. Essentially, the class pressures tear Alison and Jimmy apart,because Jimmy is so bitter by his own circumstances, being "less than" Alison and also by not being able to live up to his potential by using his education as a means to better himself. Jimmy is so affected by his circumstances that he is abusive to Alison verbally/emotionally/psychologically. They come to terms with their relationship in the end, but it is a far cry from being anywhere near a happily ever after ending and probably more out of a comfort issue they have grown to have towards each other.
You could also take the angle of relationships and discuss how relationships affect people's actions. You could explore Alison, her reasons for coming back to Jimmy after the abuse. You could discuss what pulls Jimmy and Helena together after Helena is one of Jimmy's least favorite people.