Get ready because this is a VERY long question
Okay
What do you do if a guy you have known for a long time and really like asks you out while you were on vacation but you say no because you were leaving the next day and you would'nt see him for 10 months but you really wanted to say yes and he looks really crushed by this and you see him later on that day looking really sad and depressed and looking at you while you were both sitting across the aisles from each other and he was looking at you the whole entire time and secretly you were watching him too and then you see him later on that day again because you were walking your dog and you and your friend start talking really loud about where we were going then you feel really bad about how depressed looking and embarssed about getting rejected and he just got a lecture from one of your friends about how he shouldve asked you out earlier BEFORE your last week on vacation so then you finally convince your best friend to go with you coincidentally down his street and tell him that you like him but you were leaving and tell him to ask you out next year.
Like I said very LONG question.

A long question with no punctuation marks, so your point is lost by the time you get to the end of it.
So are you asking if you should talk to him before you leave?
Yes, if you want to.

You might get more responses if you made the question easier to read. I got part way into it, and it became confusing due to lack of punctuation. I decided not to invest anymore of my time into it.