daf bit: Gittin 81
The next mishna (also on this daf) says: if a man divorced his wife and then they are seen staying together in an inn, Beit Shammai says that she does not require a second get from him (i.e. we do not worry that they re-consumated the marriage) while Beit Hillel says she does require it. Both are talking, the mishna says, about the case where they were married; if they were only betrothed (which does still require a get to dissolve), then Beit Hillel agrees that she does not need it because he would not take liberties with her in that situation. (81a)
So it seems that Beit Hillel holds that if they were married (and then divorced) he will not resist the opportunity to have relations with her (which can effect a marriage), while if they were only engaged (and then divorced) he can control himself. The reasoning is not given.
Marriage vs. betrothal
Re: Marriage vs. betrothal