Is there connection between Happy’s rejection of Willy’s and Happy’s periodic insistence that he’s losing weight and will soon get married?
Talking about losing weight and getting married are both examples of things about himself that he wants to change, or thinks are changing. They are both a fresh start. He is talking about how he is remaking himself. He wants to get past his failures and move on.
I believe so. Happy has become disillusioned with his father and reveals this to his brother Biff when he returns from out west. He is concerned about his forgetfulness, his contradictions and his treatment of Linda. In addition, Happy, as a youngster, lived in the shadow of his brother Biff, the amazing football player. He seemed overlooked and overshadowed.
As an adult, Happy still feels these same childhoold feelings when Biff returns. The focus immediately returns to Biff and the prospect of his opening a sporting goods store. Happy resorts to repeating things that he hopes will earn hims some complimentary attention from his parents. He says "I'm losing weight!" and "I'm getting married!" because he knows these things will make his parents proud.
Ironically, we know that Happy is not going to be getting married. His promiscuous lifestyle is documented through his words to Biff and through his behavior towards the girls during the ill-fated dinner scene where he lies about his brother's sports career and his own business successes in order to impress the women. From this, we can assume that Happy has not lost weight (though it is never exposed that he is heavy) and that he probably will not do so.
Feelings of rejection are difficult to overcome, as we see from Happy's behavior in this play.