Me and my father have an off and on relationship he would show up for a while then we would lose contact. I haven't spoken to my father in about a year and a half and then my half sister calls me about 2 months ago about him and drops the bomb of dementia...so I go to visit and call we have a great time then one day he tells me he's upset with me because I told him I was taking him to court and I said for what?? Then he goes on on to say he told me not to call him anymore which he never said to me...I couldn't wrap my mind around it I broke down I hated that I did in front of him but I couldn't hold it. I left calmed down we talked after and said we would work it out and still keep in touch but now he blocks me on his phone. At 1st I went out of my way to make sure we talked, popped up at his house. He was soo happy I did that but I ended up leaving upset and not wanting to go back. My heart breaks every day knowing he really believes this...a part of me wants to walk away and let it all go before it gets worse.
Only you can decide if you can deal with his broken brain behavior. It's very challenging to set and maintain boundaries with our parents, but they are a life saver.
Maybe visits can be stopped before he gets ugly, you say he's happy to see you and then it gets bad. Can you imagine yourself running in to say hi because you were close and as soon as the first word that is leading to upset, you say well as I said just stopped in to say hi, love you gotta go and leave. Don't let his words slow you down or cause you to pause. The 1st time is the most difficult, you feel rude, but I use it and it works. Sometimes I have 30 second phone calls with my mom. I can tell by her hello how it will go. I have not seen her for a couple years because I don't want to be her scratching post.
Good luck and remember you matter too.
If you can see him and talk to him if he brings it up tell him you would not do that.
**The exception being if you do have to take him to court to obtain guardianship in order to make decisions for him. Someone should have POA for health and finances and if he is not of sound mind to do that guardianship might be the only way. **
Trust me this is not the only thing he will say to upset you. This is a long and difficult road he and the family will be on. I hope you have help for him
If he is a Veteran it might be possible to get more help through the VA.