I would opt for 2. [nicely] butt into his conversations simply because this is probably a misunderstanding between your psychology and his. He probably talks more to other girls because he wants to have a conversation with several people at the same time and he can talk to you anytime, especially since you do have time for each other. Not a lot of people do, in which case, then I would be worrying, but you're fine. Also, you may be just sitting and watching him as he talks to other people; I'm sure he wouldn't mind if you popped in and said something--after all you're more than welcome to. He probably wants your attention.
You don't ever get awkward around him and his friends, meaning you don't say anything, do you? I experienced a similar situation: I have a good friend and I liked her a lot and I knew she liked me because she was always staring at me, and her friends would occasionally come up to me and leave her by herself to chat with me, just friendly, and I guess she got jealous, which she didn't need to -- it was only friendly conversation, but she never really talked to me when it was just me and her. But when her friends came to talk to me, she would always follow and say nothing, just sit there. Sometimes she would say something, but it was weird because she was never trying to talk to me directly, just get my attention from her friends, so it was weird.
Also on a smaller note, he probably likes it when you butt into his conversations; it's just something guys like.