A man who is not seeking a long term serious relationship and may want to keep his options open is the kind of man you're describing. He may want to go in between partners and not really offer a whole lot to them. You've been there for him and he finds you safe but in at the same time he is hurting you and breaking your trust.
Regardless of his age, he may not want to commit and may continue to leave this sort of life style. It would depend solely on you, what you want to do about your own situation. Do you want to keep on giving him chances or do you want to be the only one for him?