rebuilding trust?

After being with someone for over 5 years, and 3 out of the five have been nothing but arguements because he won't stop going online looking for other woman to call beautiful. He isn't sending photos, or exchanging numbers etc. however, I always catch him on it. so, for the love that I have for him, I chose to stay each time.. he promised and swore it would stop so I thought I could rebuild trust but I'm finding its extremely hard to do. any advice?