How do I know if he's really into me?

I've been dating this guy for half a year now. And the relationship was really great at first. We spent time together, and sent txts to each other all day. Now for the past two weeks things have changed. He dont answer my calls. Actually I think he ignores them. He doesnt respond to any of my txts. Now I know his work keeps him really busy and tells me he loves me and want to be with me and my son. And to just hold on and things will get better. I havent seen him or really talked to him in two weeks. Ive beem blowing his phone up just hoping for a response. Help!!!!