Unenthusiastic Wickham

Wickham and Lydia visited today and it seems to me that Wickham is not nearly as interested in Lydia as she is to him. Lydia is constantely giving him affection, while he often completely disregards her. He seems awfully unenthusiastic for someone planning to get married. I have this overcoming feeling that Wickham is up to something. I want to tell someone about this, but I also want to give him the benfit of the doubt. I feel in my gut that he is up to no good, but at the same time, I do not want to be impolite. What is the right thing to do?