my jealousy is so bad

reddit is a tiny bit scary to me despite anonymity but i feel bad about how jealous i am all the time. im in a qpr trio with 2 people, and im also in a qpr with my best friend. im aroace so for the most part they fulfill all my needs relationship wise so realistically i should feel fine! my best friend is poly and is in a romantic relationship with 2 other people. i love them, they treat him well. theyre good for him. at the same time though, i hate them. i can be reassured so many times that he wont leave me now that hes dating again but despite not being apart of that relationship, its almost like theyre moving to fast for ME (they met about a month ago and he plans on moving in with them when he graduates in spring). i feel like ive totally fallen to the wayside and i resent them and him a lot for that. he tells me all the time that he thinks of me still, and everything he does he does with me in mind, but he cancels plans on me a lot despite me being super busy and putting that time aside specifically for him. he leaves me early when we do go through with plans and when were together, he mostly talks about them. im happy hes happy, but it feels like its at my expense even though i know thats not true. i want to be the first priority again. i want to be the one he spends all his time with again. i want to be the one he pays attention to and talks to all the time but im not anymore and i cant stand it. its not jealousy towards the romance aspect (im a lesbian anyway) but its jealousy towards the place they hold in his life that used to be mine. he tells me it still is but its not and i hate it. thats not even all either and its so frustrating. one of my partners in my qpr trio recently started dating her roommate romantically and i said i was okay with it because the rational part of me is, but the disordered part hates it. hates the thought of someone else taking her away from me. shes always been more distant and focused on her academics, but with this person shes not and it scares me that shes going to walk away now that she found someone. its a mix of obsession and jealousy and fear that these people that mean the world to me are moving on and i cant go with them. i feel like i care so much more than they do