Your reaction should be one of concern (it does not seem that he is seeking long term commitment) The reasons for this may be many. 1/ he feels that he is too young to settle down, does not want to take on family and fatherhood responsibilities, 2/fears that he would be the one hurt by his partner and therefore withdraws first as a defense mechanism 3/ he truly does not know what he wants out of life and what his priorities may be. The issue here is if he indeed cannot control this behavior or that he is not willing to try. Stay on guard and try to really find out what is going on. If he does not what he wants to do, then he can take different steps to figure it out- counseling, self help/soul searching, making a list of short and long term goals, offering suggestions of what some of your contribution to his self examination may be (couple's therapy, couple's retreat, etc) Do not take it light that he is saying he does not know and when he tells you the same thing over and over. Why should you be the one in limbo?