What would make a 44 year old man who wanted a serious relationship with a view to it leading to marriage suddenly change his mind?

Can you imagine someone suddenly for no obvious reason changing his mind about a serious relationship? There is no argument involved no mention of anything, just a weird, inexplicable change literally from one day to the next. No third person is involved in this decision. It is almost as if the person has a split personality.

Even stranger is the fact that he had been the one who had initiated the whole thing, made promises of commitment and opened up the channels of communication initially. The woman’s part in this? Although cautious at first, she finally begins to trust this person and gets closer to him, expresses her love and devotion and agrees to trust him fully. Monday things are perfect, Tuesday too and out of the blue on Wednesday the guy makes a 360 degree turn and changes completely. Can someone’s serious feelings be transformed so suddenly? Looking at his age it’s not as though he is going through adolescence! How do you see it? Shouldn’t he at least give an explanation or even some kind of excuse no matter how lame it may sound? By the way there is NO pressure from the woman, no hurry for anything.