I periodically do the same (send a message to both loves at one time) but always something along the lines of "traffic is bad-running late xo"
However-I agree completely with Nyc-if you are going to navigate relationships of any kind well-you need to be able to speak your needs clearly and concisely.
As Galagirl says-we aren't mindreaders.
So-tell him that you would prefer no message to having a dual message. THEN ACCEPT that may mean no message.
My husband would prefer no message over a dual message-so, frequently he gets no message because I'm not inclined to send the same message twice.
My boyfriend prefers no text over a dual text because it screws up his phone-so frequently-he gets no text because I'm not inclined to write it twice.
"Love As Thou Wilt"