Dad has become unrecognizable

I’ve posted here before, but it’s been quite a while and some new things have come to light. My dad is in his late 70s, I’m early 40s. Unfortunately, we lost my mom several years ago to cancer and it was very tragic.

About a year after my mom died my dad became very friendly and started spending a lot of time with a married woman down the street who is taking care of her mother, she normally lives in another state where her husband and son reside. She is 20+ years younger than my dad. I saw some red flags early on when he shared that she would often vent about her husband when they went on walks or hike together. She would share text messages and emails he had sent. This all came to a head a little over a year ago we got into a pretty big argument because he was gradually pushing everyone else out of his life, including long time friends and myself, my husband and my son (his only grandchild).

Fast-forward to recently, I thought we came to an understanding where I don’t need to hear about him getting together with this woman, but we needed to work on our father daughter relationship, and his relationship with his grandson. He seemed to agree, but instead, what he did was run to her and share everything I had talked about, including my concerns about her motives. I told him I felt very betrayed and that he broke my trust by sharing what was a private discussion between him and I. I also told him that he has gradually been pushing me right out of his life while insisting that his family is the most important to him. His actions and words don’t match. He said if I stop talking to him, he will end his life. This is not the first time he has made SI threats, he has a counselor and has told his counselor in the past about it but because he had no “plan“ it was more something they were just monitoring.

I am at a crossroads of trying to decide if my dad is this manipulative person who is emotionally abusing me and playing mind games or is he suffering from some cognitive decline and has imagined this emotional affair with this woman all in his own head. He claims she has never expressed romantic interest towards him. I don’t want my dad to be taken advantage of, but I also have to protect myself and my own mental health as it has taken a real toll on me.