After a result that saw his side's faint LaLiga Santander title hopes extinguished, Koeman said the match reflected what he had seen for much of the season.
"If we speak about the first half, it is a reflection of what has happened to us in more than one game," he said.
"We played well and with opportunities and they have one attack and you head into the dressing room at 1-1 and this is very hard mentally.
"The second half wasn't so good.
"In the end, it was 2-1 to them and this always happens in moments when you don't have that luck."
He declined to comment on what this result would mean for his own future.
"I am not going to answer because I already said yesterday what I thought and I do not need to repeat myself," he said.
He went on to reiterate his desire for club captain Lionel Messi to remain at the Camp Nou this summer, especially given his importance in front of goal.
"We hope [that Messi doesn't leave] because he is still the best player in the world and he has demonstrated today that it is impossible to play without him," he said.
"He has now scored 30 goals which have given this team many points.
"It is a question for him.
"For me and the club, we hope that he continues with us because, if we don't have him, we have doubts over who will score as many goals."
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