In your case, it is NOT LOVE. it is time and time again of EXPLOITATION, MANIPULATION AND EMOTIONAL BLACKMAIL.
my dear friend, you have a soft heart and he knows that that is why he taps on that every single time you find out about the affair. You want someone to dictate your life through emotional blackmail or you want to stand up for yourself with a backbone and say enough is enough?!
I know taking the first step is NEVER EVER EASY. Nobody said it was easy. Take an analogy of buying 4D/TOTO, if you never buy, you never know if you will strike or not. The chances are if you buy, the probability of you striking is higher than not. Drawing similarities, take the first step to BE SELFISH FOR ONCE and do SOMETHING FOR YOURSELF. step out of it. Chances are you are either happily single or he will realize the impact of the loss of you and things might get back on track (which i hope maybe not but there is a chance).
Sometimes, having the taste of losing something will give one a super rude wake up call and realize the impact of the loss and yearning. You need to let him know YOU USED TO LIVE FOR THE BOTH OF YOU, NOW FOR GOD'S SAKE LIVE FOR YOURSELF. Who knows, give it two or more months of hibernation and separation period, he might realized the loss of you is hard to bear and he might "actually try?" I am NOT sure of the chances of that but hey, everything you take is a gamble. Either you put your right hand in, or your right hand out.
At the end of the day, all i am saying here essentially is STOP BEING A SADOMASOCHIST and continuously TORTURE YOURSELF over and over again. Think for yourself, be RESPONSIBLE for yourself. If you can't even love yourself enough to not want to HURT yourself, then what capabilities do you have to say you love him?
P.S: erm... this ain't suppose to sound so angry or offensive with the CAPS. just emphasizing the important things i wanna say.