import re
rex = r"\s+(?=\d{2}(?:\d{2})?-\d{1,2}-\d{1,2}\b)"
s = "2018-03-14 06:08:18, he went on 2018-03-15 06:08:18, lets play"
print(re.split(rex, s))
aW1wb3J0IHJlCnJleCA9IHIiXHMrKD89XGR7Mn0oPzpcZHsyfSk/LVxkezEsMn0tXGR7MSwyfVxiKSIKcyA9ICIyMDE4LTAzLTE0IDA2OjA4OjE4LCBoZSB3ZW50IG9uIDIwMTgtMDMtMTUgMDY6MDg6MTgsIGxldHMgcGxheSIKcHJpbnQocmUuc3BsaXQocmV4LCBzKSkK