Have you sat down and had a conversation with him to find out why? Are there problems in the marriage other than this? Communication is key. There may be other issues such as the relationship fizzing out, lack of creativity in the bedroom or the flirting is gone. Try to find out what the issue is without coming across as angry or accusatory. There a site I came across with lots of info called www.rescueyourmarriage.info that send you useful tips on how to save your marriage when its heading in the wrong direction. Hope this helps.