Dad thinks I am my mom

I need recommendations on how to deal with this ... dad called me tonight in tears saying how much he missed me and wished we could still be married. I gently said, daddy, it's me, your daughter. I think you might be thinking about mom...I tried to change the subject, tried to talk about what a great marriage he had with mom, told him I was married and had been married to my husband for 40 years...nothing worked. I am the only family member locally, my sister passed away in 2023. We live about 20 mins from his facility so I am able to go visit several times a week. Do I stop going to see him so often so he isn't getting confused about my regular presence? He has become very dependent on me for most things, calls me about 10x/day so I can see how this would be easily confused and I look very much like my mother! If you have experience with this, how long did it last? Is this a "phase" or just a behavior that has to be managed? When he was hospitalized before moving him to the community he lives in now, he thought I was his wife then as well. It's so hard and makes me very sad to hear him crying and grieving my mother who has been gone since 2012.