BF of 18 months spends hours a day texting ex-gf. Says he has never loved anyone like he loves her but that they are no longer together. Is this healthy?

My BF has PTSD from tragic loses in a short period of time in his immediate family. A gal who lives several thousand miles away was his HS crush and he dated her briefly after his divorce. She broke it off with him and they had little to no contact for a couple of years. She recently started talking to him again after a tragic loss of her own. It has been 6 months and he texts her every day and makes no bones that she is the great love of his life. I told him to go back to her and do what it takes to win her back and I would step aside. He said she didn’t want him and they were just BFFs. I don’t think constant contact with her is healthy. I think it distracts him from our relationship (or any future relationship he may endeavor to undertake) but given the mental health issues with PTSD I don’t think he will stop on his own. Am I going to get crushed under the weight of his inability to let this woman go?