What are some ways to help get over this? PLEASE READ!?

My crush(my brothers best friend that I`ve known as long as I can remember and hes known me ever since I was born) got a new girlfriend about 5 months ago. And it hasnt rele started to get to me till now. I mean I know I cant date the guy(almost 5 years older than me) but I felt much better about when he WASNT dating this bratty high schooler. And I dont just say she is bratty because my crush is dating her, she is very bratty and so is her whole family. And my crush(BTW my crush and I r rele good friends he thinks of me as his little sis) is starting to change. He doesnt talk to me like he used to or hang with me like he used to. He is ALWAYS with his girlfriend. And it feels like someone is biting on my face and shooting me through the heart when I see them together snuggling or wut not. What can I do to get over this. I hate it! I mean my mom always said if I cant date the guy we can at least be good friends and he doesnt even hang with me no more. For the record, everyone on planet earth knows I love him so he already knows and his girlfriends(sweet...NOT) little sister always has to make fun of me about it. I ignore her most times though. How can I get over this? I cant take this anymore. I cant keep feeling like this. Help.