My spouse looks up dating sites

Ive noticed that my husband has been logging onto dating and sexual encounter sites. We have been together for over 13 years. Do you think its the itch for something someone else? At what point does this start to happen in a marriage. We have 4 successful businesses,houses,nice cars. Is it me? I try to do nice things. What can I do to spice up our love life? Im so confused and hurt.