Getting jealous of my best friend getting close to someone

So there’s 3 girls in my friendship group, me, My best friend and another girl. Let’s just call my best friend S and the other girl J.

we’ve remained as a group for a long time a bit more than a year but me and J have never really been as close as S and J. S has been my best friend for 3 years so far. But lately J has been getting the attention of S. the attention that I usually recieve and ONLY recieve. I know my place I know my title but I’ve been feeling incredibly upset over the past 2-3 days as they’ve been lowkey ignoring me sometimes, paying more attention to each other. I try to handle my jealously but I can’t.

S would always tell me she loves me ( this may sound a bit wierd but it’s what we say and how we bond), we’d have each other as our lock screen and home screen and we would tell each other everything but now S has included J into each one of those, and it makes me feel less important now