Boyfriend and mixed signals

I've known this guy since October, liked him the whole time, he seemed really cool, easygoing, I fancied him etc. It turned out he felt the same about me and he asked me out about 6 weeks ago. It was great for the first week, we saw each other every day etc. He said he really liked me, was so happy I was going out with him etc and that he wanted us to be open with each other because he'd been hurt in his last relationship. Fine with me, sounded perfect. About 2 weeks later we were at a party, I wasn't well (was starting to go down with a serious throat infection, didn't realise this at the time) and wasn't as attentive or whatever as he expected me to be. I just wasn't in a very good mood. I could see him losing patience a bit and we ended up having a fight outside, he said he wanted a girlfriend, not a mate, that he was putting in lots of effort with me but getting no warmth back, etc. I was shocked as that wasn't what he was saying before and I didn't consider it true. I actually cried because it was hurtful, and I wasn't feeling well at all. The next day we met to talk about it, he said he just meant how I was behaving that night, not in general, that he didn't realise I was so sick and that he was really sorry. He brought me flowers to apologise.

Everything was good after that until last week when he texted me asking if we wanted to watch a film together in my room. I said I was very tired, I would be bad company etc and he took it that I just didn't want to be with him and got annoyed. I ended up inviting him anyway because I didn't want to leave things like that between us all weekend. He said he'd got upset cos he felt like I didn't want to see him, he wasn't a priority for me etc, which isn't true at all. I told him that and everything seemed to be OK. But it's still bothering me that things can go from so great to so bad so quickly and I'm constantly reassuring him that I do really like him. I think he's wary of getting hurt, but so am I. I'm finding it difficult to really trust and confide in him knowing that he can go from saying I'm wonderful and he adores me to being pretty cold. It's like a vicious cycle!

Since the 2nd fight (which was really just a misunderstanding I guess) we've spent more time together, he's stayed over and we've done some sexual stuff. I really enjoyed it and I think he's realising now that I'm serious about him because I'm not the casual sex type. We haven't actually had intercourse yet - I'm kind of holding out a bit to make sure it's a long term thing. How do I say this without offending him or being misunderstood?
Also, how can I actually show that I really like him? I've never been good at expressing my feelings so he's probably right to feel a bit underappreciated. I just feel really stupid and corny when I try to say something nice or give a compliment. I'm trying to be more touchy feely but I don't want to overdo it or anything, I'm just not used to being like that with people?! Help appreciated!