"he feels like no-one loves or cares for him"
Put that into actual feelings and imagine for a moment what it is like for him. Lonely? Sad? Jealous?
Now imagine if he had said to you "I feel lonely, sad and jealous"
Would you have replied in the way that you did, telling him it's not true?
You need to empathise with these feelings. They are real.
My DSs are almost 8yo and 3.5yo. They share a room and I know that DS1 looks forward to the time when DS2 is asleep. I get into bed beside DS1 and we cuddle up and have "special chat" where he gets to choose what he wants to talk about.
Sometimes it's just Star Wars and stuff, but quite often, he will open up and tell me about things that happened at school or what his friend said to him or whatever. I also ask him if anything is worrying him. Most times the answer is no, but sometimes he has poured his wee heart out about things that seem small and trivial to adults but that really mean a lot to children when it is happening to them. I empathise with how he is feeling and we talk about how he can find a solution to his problems.
The key to this is trust. He trusts that I am not going to tell him that he mustn't feel that way, or that he doesn't really mean it or whatever. So for example, he says he is angry that his brother broke his Lego model, I would say something like "yes, I really understand why you are angry. I would probably feel angry too. You spent ages doing that model, I know how important your Lego is to you. It's hard at this age when your brother doesn't really understand how much work you have put in. But just imagine how much fun you will have with him when he is older and you can build together." I remember that the solution to this one time was to take pictures of his models. His main concern was that his brother would smash the models and he wouldn't remember how to put them back together. These were models he had made himself btw, not a kit.
It sounds like we chat for hours from that description, but 10 minutes is about average, unless there's something really bothering him. It leaves him feeling that he has been heard and that he is loved and cared for (he has told me this)
Sorry to talk about us for so much of this post, but I don't really know how to explain what we do other than by giving an example. I hope you find it helpful.