Frequent client wants more

I have this one client. He’s one of my most frequent customer. We’ve comfortably chat about my works, his works. He also shared with me some helpful inputs in term of Marketing for my business. I consider him as a friend.

But lately I realized that he kinda wants more with me sexually, maybe emotionally, which I don’t want. He also told me that he got jealous when I told him I was seeing the other guy. I really don’t want thing happens this way between us. I told him that I just think of him as a friend. He seems unhappy.

What should I do? Or what should I say?