Help me

I've been dating this guy for a year and a half, but recently, he's lost interest. I will admit that I haven't been trying very hard myself and that recently I've been kinda bitchy towards him, but it hurts. He's in love with my best friend. He even admitted it, but I still want to try. One of my friends have been telling me that our relationship is really toxic and that I should leave because this isn't the first time our relationship has been on the edge and we've been doing the whole "1 more chance" gig for months, but I really want this to work. Do you think it's worth it? Honestly?