Boyfriend of 5 years doesnt ever want to get married

Im not sure how to feel about this. We have been together 5 years and have a 2 year old daughter and a little boy on the way. Since ive met him hes always said "i cant wait to marry you" always called me his wife, and would talk about our future being married. Now he says he doesnt want ro get married, not now or ever. Im someone who has been dreaming of my engagement/wedding since i was little. I cry watching engagement videos hoping itll be my turn soon and now all of a sudden he doesnt want to get married. I asked why and he basically said hes worried in the future ill cheat?(never have never will) and he doesnt want to be stuck paying alimony. Im pretty upset, not sure what to do or think. I dont want to be with someone who never plans on marrying me but i obviously cant just throw away 5 years for this. What do you guys think?