We know from Chapter 3 that Edward is what we would call 'shy.'

"his manners required intimacy to make them pleasing. He was too diffident to do justice to himself; but when his natural shyness was overcome, his behaviour gave every indication of an open affectionate heart."

Perhaps, after this absence of some weeks, he feels shy again. That could explain his not writing before the visit and his embarrassment at being with other friends. He might not have written because he did not know if he would follow through on the visit or not, once it came to the point.