One no one mentioned is maybe he is a nice sweet guy that saw a friend hurting and chose to be there but has other things in his life including a possible significant other. Seeing you were back and not needing help anymore, he returned to his life.
He may have never meant for his friendship to become a more intimate relationship or as suggested by others he questions the rightness of it.
Ask him to meet you at a nice neutral location, possibly a restaurant near his work and close to the end of his work day. This will not appear to be a possible date as no one goes directly from work to a date, you always at least clean up. Have a relaxing dinner and ask if there is a problem. Let him know you are not trying to force an issue but you would like to know if he is interested in a relationship, because you are, but you are willing to just be friends and look elsewhere if he is not.
He might be interested but have perfectly valid reasons for not pursuing it or appear to be pursuing it at the moment. Emergencies, including work emergencies, happen and if your relationship had been casual and no planned time together were interrupted, he just may have not considered calling. That is not rude or ignoring you. Consider, do you call all your friends and/or family when something comes up? No, you only call those you are expected to meet and or help. That does not mean you do not care about the others or indeed love the others. Men are like that, only moreso, they only start really telling what is going on that might interfere with shared time if they are already in a relationship.