Boyfriend dumps me and tries to go back to a ex after 11 years?

I have know my ex boyfriend for 3 years and we have been serious off and on through that time… one week he is talking marriage to me and 3 days later he breaks with me saying he wants to try to give his ex a try cause he still has feelings for her and he broke up with me because it wasnt fair…. confusing… will this possibly work out for him? or do you think he will come crawling back?