Delivery receipts are nice - but all they mean is that the recipient triggered the return receipt. He can open the message, then immediately close it - and you'll still get a receipt, even though he never read it.
The safest way is to ask the recipient to text you when he gets your text.
Delivery receipt is an indication the message was delivered, not that it was viewed. Also, the option to send any type receipts is normally defaulted to off. So unless the recipient has turned it on, your not getting a response.
As mentioned above, ask for a reply is the best way to be sure.