No, you aren't trying to control his behavior, but in his mind, you are attempting to control his time and where he needs to go, etc.
It's very difficult for single parents because the spouse that is out to lunch isn't there to help nor can you rely on them. Do you have any friends that can assist w/the babysitting or a network of mothers in the church or neighborhood that would be willing to work with you on the babysitting issues?
You could phrase your questions by saying "H, we have run out milk and the children need it for their cereal and some of their favorite meals. Would you pick up a quart of milk for them on your way over? If it is too inconvenient, would you stay with the kids while I run out to get the milk?" You have to give them some options to think over decide on their own which way to respond. When you give them the freedom to decide w/o pressure, they generally will go w/the easy option. It is called putting the ball back in their court.
Try to remember....you can't rely on him to do the right thing because he's a kid himself at the moment.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
