He did, but it became "lean over" after out of early states all but one (NH) voted for Hillary, and his viable path to defeat disappeared after an early March primaries. The primary schedule always favored Hillary (with the entire South already voting and playing a large part in providing her with a lead in delegates).
Not over till it's over, but realistically yes it's over.
Well, of course theoretically it's not over until she reached the magic number, and it's even more theoretically not over until she's formally nominated, but barring a major scandal breaking before that point or her (not very likely) death, Bernie has no viable path to victory.
Sanders should never have run, all he has done is waste a massive amount of money on a campaign that was never going to work. Lots of the republicans should never have run either for exactly the same reason. They are just ego driven deluded fcukheads.