Guy issues

So I love the relationship I have with my boyfriend, but unfortunately his best friend seems to be part of it too. Me and his best friend do have a history together, we never dated, but we definitely had a thing. Its really awkward because both my boyfriend and his best friend flirt with me. Don't get me wrong-- I love hanging out with them, and getting all the attention is great-- I'm just confused why my boyfriend isn't the slightest bit concerned? Like why doesn't he want alone time with me? I really just want a relationship with one guy....... But I kind of feel like I'm in one with two....... What should I do?