Okay so I like this guy but I don't know how to tell him?

Okay so I like this guy that I've probably known for I don't know, 2 weeks now? And I really like him. I haven't seen him in a week but I have his e-mail and we e-mail alot (He asked me for my e-mail if that helps at all). He has a girlfriend and I really hae that but I guess I have to live with it, so anyways how do I tell him? I'm like super shy and stuff so yeah. Could you please help me? And no bogus answers okay? Please? This is super important!!!