Hi Girly - it sounds like the affairs were not just a one-time thing. Given all of that it's quite reasonable for you to feel doubtful. I can also relate to your pain - I've been crying a lot too. More than I think I can bear. I think what you have to do is look at whether he's really showing you he wants to change anything that would stop the behaviour. Maybe he is just having his cake and eating it too - as many are inclined to say here on this board.
Also, there may be a betrayal bond at work here. It's been found that those who continue in painful relationships where there are also intermittent loving times have a greater intensity of bonding due to shared trauma. It's similar to Stockholm syndrome. There's a whole book called "The betrayal bond." If that's the case, then time away and other supports can really help regain perspective and help in determining what a healthy relationship should feel like for you.
Especially if you don't have a long-term marriage or children involved it doesn't seem reasonable to expose yourself to such a high risk of being hurt again if he is a serial cheater unwilling to change his ways.