I suggest that you stop soothing him when he cries. I think that when he cries it is a form of temper tantrum, just a different form of tantrum.
If you ignore him every time he cries (I know it will be hard) each time he cries his crying time will be shorter and shorter.
I suggest that when he cries you walk out of the room. If he cries and follows you, walk into a room where you can shut the door. He will be fine.
This is not cruel or tough love. This is looking forward to making him into the eight year old you want him to be. An eight year old boy should not be soothed every time he is frustrated.
Love him with big hugs when he has completed the task you have set for him.
He will only become more independent if you require him to be more independent. Soothing him when he cries will make him dependent on the soothing. That is something that you don't want him to be.