I want it to be very subtle that he takes a double take and reads it over and over again
What can I send to him in a text to subtly tell him I’m thinking about having sex with him?

You don’t do it subtly. You do it directly and explicitly
Then he’ll think I’m class less and ignore me
Send him a pic that Is revealing yet leaves something to the imagination
Opinion
2Opinion
Mention laying on your bed butt naked and wet.
Tell him your panties are wet :)
Superb Opinion