Why did he do this? Male opinions would be very helpful please but womens also welcome :-)?

I fail to see what you are complaining about, you ended the relationship, did you expect him to put his life on hold while you made up your mind whether to have him back or not, he had the opportunity to start a new relationship with another girl and I see no reason why he would turn that down, he did not know that you would want him back, in fact you had told him that it was over between the two of you, you don`t like the fact that he was not crestfallen and heartbroken because you dumped him, that is what you wanted him to feel, you wanted him to come running back to you at the click of your fingers and all would be well again, well, he has shown you that although he loves you he is not prepared to have his life ruined by you and he can still enjoy his life without you, you hurt him by dumping him and now you want him to feel guilty because he met someone else, the way that you are feeling is your own fault because you were the one that caused it, be happy that he is back with you and start again without looking back over you shoulder at what happened when he was single, because that is what he was.