Backstory: I am female and one of my best friends is someone I dated briefly (say, 2-3 months) about a year and a half ago. We got on really well but there was no real passion. He broke it off with me, I was pretty upset for a few months and we didn't talk much, then he and I started seeing other people and we became very close, as friends, after the dust settled. Our friendship was admittedly a bit ambiguous for a while when we were both single at times and leaning on each other as a distraction from our dating problems (yes I know...not super healthy, but not that unusual?), but it was made clear that we would never again attempt a relationship. We stopped the ambiguous portion of that relationship last summer and have had a completely platonic, non-romantic, non-sexual relationship ever since.
My issue: I met a boy around the time my friend dumped me. This person and I became friends and started seeing each other romantically about 5 months ago. I really love this guy and I think he loves me. I'm determined to be in a healthy relationship with him, but my aforementioned best friend is getting in the way. My boyfriend is not comfortable with our situation; he understands that we are just friends, but, because of our past, I think he thinks there is still some sort of intimate/romantic interest there and it's putting a huge barrier between us that's preying hard on both our insecurities.
I understand where he is coming from. My best friend recently moved pretty close to me and, in the past, he and I did everything together most of the time, even just as friends. Now, things are different. My friend and I see each other much less frequently (as we're both seriously dating other people and we're more interested in spending time with them, of course) and I've tried to create obvious space between us to illustrate to other people that we're not "together". I still enjoy spending time with my friend and we care about each other as family, but my boyfriend gets priority when it comes to my time and energy and love.
There have been a few incidents and misunderstandings in the past months in which my boyfriend's become convinced that I'm giving my best friend priority over him and I don't know what to do. I never cheated, emotionally or physically, and have no interest or intention of ever doing so. My current boyfriend questions my motivations and the motivations of my best friend.
I realize this is a pretty obvious pickle, but it's just how everything's unfolded and I'm honestly not romantically interested in my friend any more. I only have eyes for my current bf, but I do want to maintain my friendship on some level. I don't know what actions to take to make this clear to my boyfriend. He has insecurity issues and I think he needs to work on those, but I think I need to do something too to make him feel supported.
Is this a lost cause? I feel that there must be some way to keep both people in my life if I alter my behavior and redefine my relationships, but I'm not sure how.
Thank you for your help.
eta: I feel like I should describe the two of them to shed more light on this sitch. My ex/bff is an extrovert and a social butterfly. He comes off as super-confident and he draws a lot (A LOT) of attention to himself (and in turn, he has drawn a lot of attention to our short-lived relationship/current friendship). My current boyfriend is very introverted and tries not to draw attention to himself. He prefers to keep his relationships/our interaction more intimate/private. I do not prefer one of these personality types to the other, but the former situation has caused me a lot of issues within my social circle because people (including, understandably, my current bf) have a lot of misconceptions about my ex and me. I hope that makes sense.