hii, sooo in one of the last chapters Blair was found by the cop dude who she had a good relationship with. In the last chapter, Matteo sacrifices himself for Blair and throws himself off of a building, killing Enzo in the process. That happened after Blair found out about Enzo blackmailing Matteo, which was the reason for her to be angry at him since he started acting weird towards her. In the epilogue she visits Matteo’s grave with his and Blair’s son Tommy (named after Matteo’s best friend Thomas). She then goes back inside where the cop from a few chapters before is waiting for her since they got married a few years ago (epilogue is 18 years later). She still believes Matteo was the love of her life though and she’ll never forget him. Also Nate died (killed by Enzo). Meaning all three of them died which is why she ends up with the detective who got promoted to captain of the police department.
I hope that helped a bit and wasn’t even more confusing hahahha