Yes, it does sound like your H bounces back and forth. Being brutally honest here, but why shouldn't he? He has both you and OW ready, willing and able. Sure one or both of you may put up a fuss for awhile but he knows eventually he will wear you down. So, now that you know past history...what are you going to do different this time if/when he comes back? Verbal ultimatums wouldn't be enough for me this time. Also, how many times will you take him back?
The child will always be between them and it is sticky but manageable.
Me: 46 FWS: 36 Married and Divorced 4/07, Pregnant 7/07,False R 7/07 Baby Girl born 3/08 Kicked him out because OW: 7/08 5/10 He realized what he had and lost. Moved home! REMARRIED 3/14/11!!