How do you think he'll interpret my saying I miss him?

Texted the gym trainor that am lazy to hit the gym but I miss him. We met 3 months ago but he started helpfully obliging only last month when we saw each other again. During the 2nd meeting, I felt he was a little flirtatious but didn't bother with it (I find him cute). We're not close, also because I 1st put boundaries & so we're just more of just acquaintances friendly with one another; he has shared (when I asked) that his girlfriend exchanged him for another guy. His FB profile still says "in a relationship". Normally, he answers when I send a text (which is very seldom) but didn't this time. Am thinking the next time we see each other, he might try to see how I would respond if he flirts with his behavior. But what if he doesn't? How do I maintain his wanting to help me just in case he backs off from the friendship? I don't want things to change.