Why is he doing this? My bf's acting weird..?

For the past few days my boyfriend has been acting strange. He’s been quiet but when he does talk he’s saying that he’s a complete waste of space and that no matter what I say he will not change this view on himself. When I try to comfort him or ask him what’s wrong he just tells me he doesn’t deserve me, that I’m way too good for him and he’s surprised I can put up with ‘someone like him’. I don’t even know what he means by that because he’s one of the most amazing people I’ve ever met, and I love him dearly. I feel like he’s pushing me away, but when I ask him about it, he’s surprised, hugs me and tells me I’m his girl and he wants me in his life forever. He’s also been really insecure too, last night I didn’t go on msn or facebook because I was busy and I woke up to a barrage of texts asking where I was which progressively turned into the likes of “are you with someone else?”. So does anyone know what might be going on with him? One minute he’s acting cold, depressed or untrusting toward me and then the next he needs me so much and can’t stop telling me how much I mean to him. Confused.