Why does this guy always ask me if I have a boyfriend?

He's always flirting with me, he is 35 and I'm 23. He has told me I'm attractive and have a nice body. At times he has slapped my bum and said sexual flirtatious things to me. Sometimes he doesn't say much, just says hi and askes how I am.

Most of the time he askes if I have a boyfriend or if I've found my future husband or if I'm sleeping with anyone. One time when I was where he worked he made his friend sit with me and told me his friend is interested. He put his arm around me and said to his friend "look at her she is f*cking gorgeous"
He found it funny that I didn't like his friend and he asked why I'm not interested in his friend.

Why is he acting like this?