Help? It’s complicated!!

So my Bestfriend just broke up with his girlfriend and 4 days before that my old girl friend broke up with her boyfriend. It’s complicated.. I’ll fill you in so my girl friend D broke up with her boyfriend (who is my ex boyfriend) they dated for a year and 10 months.. S my Bestfriend he broke up with his girlfriend bc they did have time.. soo

I have had a crush my S my Bestfriend for a long time now and I think D likes him... See the thing is I’m jealous and scared that D is going to take S away from me bc she did it to me before with my ex (our ex now) so I don’t know what to do. S knows I like him he always knew.. I only just became friends with D again.. What should I do?