Can someone fall out of love instantly?

My boyfriend professed love and I think he was genuine. He came over for dinner - everything was great. He intended to come back later after a meeting. I called & said I needed some alone time, let's skip the later visit. I then changed my mind & later invited him over. He came and said he thought I was going to break up with him - he was having doubts as to if I was the "one" - and that all his feelings for me had evaporated - just diappeared - as if struck by lightening. This from a man who a few hours earlier had been happy in love and talking marriage - any thoughts on what happened?