my recent FP is currently in a relationship with someone else and it's honestly quite debilitating to me- i feel like i am really dependent and needy for his attention and affection(which he does give sometimes and i get euphoric on it) yet i have no choice but to restrain myself from reciprocating cuz he is dating for gods sake and it feels very wrong and selfish for me to do so. whenever he expresses his love and how much he misses his partner to me i feel numb and drained- why cant he show this to me instead? 

it is a horrible trigger for my mood swings and bpd traits and ill instinctively guilt trip him or try to make him feel bad ("it must be nice to have someone you can truly love, isnt it?" or "i'll never find someone at all, ill stay single forever!"), and most of the time ill feel bad for saying it and try to distance myself in a bid to recuperate. honestly even though i want them to succeed i cant help but feel a sense of jealousy and envy within me and i kinda know the only way for me not to feel this anymore is to not make him my FP, but how would that be easy? i need advice cuz i still want to be his best friend and cultivate a platonic relationship while not letting this get into the way.