Be aware of his daily schedule, so you don't interrupt meetings with your calls or texts. Since he wants to catch you when he can, he'll be happy to give you a copy of his schedule. You want to plan something last minute? Hahahahehehehehohoho!
. . .
I've been really busy. He's too busy for you. And some days are legitimately too busy to fit any additional plans into. There's a really high chance that the "too busy" guy or girl isn't any busier than the rest of us.
And we're all used to using that 24 hours in a day in specific ways, which we would probably consider as "busy. And just like that, I've spent my 24 hours staying rather busy without batting an eyelash.
However, should the opportunity arise for me to spend time with someone who doesn't quite fit into my routine, I have one of two options: I can either shuffle my schedule around to accommodate him, or I cannot.