The very thing the man was most trying to avoid - his girlfriend cheating - by having his girlfriend spend less time around other men and her friends is the very thing that he basically creates by cutting her off from her sources of joy. By reducing her positive sources of happiness he drives his girlfriend to find maladaptive, non-constructive sources of happiness. 

The real success is in sticking your heart out there and loving and choosing to NOT live in fear. For, again, all of life, every decision boils down to that fundamental choice: fear versus trust. It's not even fear versus love, really. We all feel love and want to express it; it's our natural state. But what keeps us hamstrung, what keeps us from expressing that love is that we fear getting hurt. We fear that we won't be okay, that the pain will be too great, and that we just explode or die from the pain.