I don't want to lie to my son but I feel like I don't have a choice

Hello, I could really use some advice without judgment of my situation.

I got my cat over a year ago from my sister, who became very ill and could no longer take care of her. My cat is 3 years old, so she's not a kitten. I've had my cat for over a year, and while I love her dearly, I can't take care of her anymore. She is a Persian and has very thick long fur. I have severe arthritis, which has gotten significantly worse over the last year. I'm now physically unable to fulfil my cat's needs, and have to get my son to help. This isn't a situation where I bought a cat without realising how difficult it would be. I took her in to help my sister, but my arthritis has gotten so bad now that I can barely bend over or lean down to feed her, brush her, or empty her litter tray. I do manage to do these things of course, I won't let the cat suffer, but I'm in constant pain, even with painkillers and medications.

My son is almost 13, and autistic. He adores our cat, and is good at taking care of her, but I only see my son on weekends due to his school being far away and his dad lives closer. So during the week, I'm on my own. I'm struggling to take care of her long fur and keep it brushed to prevent mats. I've had to pay out a lot of money to take care of her, vet bills and supplies etc, but now I'm struggling financially too. I'm living off benefits because I can't work.

Here's my issue: I have a lady who wants to rehome the cat, she seems really lovely and genuine, and is coming to meet her on Thursday. She's travelling a long way, over 200 miles. And if the visit goes well, she'll be taking the cat home with her.

When my son got home from school today, I spoke to him about this and told him about Thursday's visit. I told him it would be OK for him to take the day off school on Thursday so he would have the chance to say goodbye to her. He became angry and upset (even after he'd been told weeks ago about the need to rehome her and had even talked about wanting to get a new pet after she's been rehomed). He then told me that he wants to be there on Thursday because he wants to 'talk' to the lady. This has me worried that he's going to make the lady feel guilty and not take the cat. I'm scared that he's going to get angry with her or guilt-trip her into letting the cat stay with us. But he's not seeing how unfair it is to keep the cat here, when I can't take care of her fully.

My son's autism prevents him from understanding emotions in other people and himself, so he doesn't realise how selfish this is of him. It's not his fault of course. So I feel like my only option is to lie to him and tell him the lady is coming Wednesday instead, but only tell him this after he's at school on Wednesday morning.

My fiance has suggested that I tell him he can come by on Wednesday to spend time with her before she leaves, but he will still know that the lady is coming Thursday, so on Thursday he will refuse to go to school, and will forcibly make his own way to my house on Thursday. He is a big, stocky young man and I cannot make him or force him to do anything he doesn't want to do.

I really don't want to lie to him, but I don't know what else to do.