My friend loaned me 5 to get out of a pickle. Unfortunately, he is in a situation where he needs the money from me ASAP and I don’t have it Can he sue

The answer to "can he sue me?" is always yes.  More importantly, from what you've written, it appears that your friend would win.  There is no question that you had a loan contract by which you were to repay him, and such a contract does not need to be notarized or even written.  Where no date for repayment is agreed to, Courts will imply a reaosnable time period for repayment, whihc would almost certainly be less than a year and a half.  Also, the Court would probably include an award of interest from the date it holds that the debt came due.  The outcome might be different if you said that the agreement was that you would repay him upon the occurrence of a condition, such as you beginning to earn a certain amount, but you haven't written anything about any condition for repaymentk, and if it wasn't in the written agreement, the Court will probably hold that it isn't part of the agreement anyway.