Why do I get nervous when I have to talk to my boyfriend?

Well, I can't even call it nervous, but something happens. When I'm buy myself, or talking to anyone else about the situation, my thoughts are so clear, I'm eloquent, articulate, whatever you want to call it. But when I have to talk to him, something happens. I can't even get up the nerve to say I need to talk, then when I do, I fumble over my words, I sound stupid, and I never end up getting my point across. What's up with that? Oh, when I say talk to him, I don't mean ordinary conversation, I mean serious, we have a problem we need to discuss now type of talk.