Dating My Friends Ex?

Is there any way to maintain a friendship with a friend who's ex you're now dating? My best friend who lives in Florida, broke up with her boyfriend (now my boyfriend) who lives in Ohio, near me, last year. He and I were good friends while they were together and a few months after they broke up we realized we had feelings for each other. We've been together for three months now, and my friend and I have quickly drifted apart. I talked to her about the whole thing in the very beginning, just to make sure she didn't have a problem with it, and she said she was really happy for us both! She said she always thought we'd make a good couple, and used to joke with him about me being better for him than she was. But now we hardly ever talk or text unless I initiate the conversation. My boyfriends sister, my friend, and I used to be inseparable. We were the #friendgoals on Instagram. We told each other everything, and were so so so close. Now the two of them are alienating me, or it feels that ways anyway. It hurts. They are, or were, my only friends. I don't want to tel my boyfriend about how I feel, because I don't want him to think I'm jealous of his ex and mad at his sister... I don't want things to get messy, I just wish I had my friends back. And don't get me wrong, my boyfriend is better than any best friend, but it hurts knowing I can't confide in them about how he makes me feel, how happy I am with him, and how much I love him.