Please do "not" blame yourself for this in any way. IMHO, what he is actually saying to you is that he is having self esteem issues with you and would rather find someone younger that he can feel "more than" or "superior" with. The way this relationship began to tumbul when you moved in together means, he really is not ready to actually "be" grown up and more committed. You know, that is not going to change with a walk down the isle and if you think you are stuck now, if you have children and tie the knot, you will be so much worse off.