I think Robert is completely playing Aaron. All he cares about is people not finding out about his involvement in Katie's death. He wants to control Aaron and he knows by declaring his love, he'll keep Aaron under his spell.
So who sent Darren that text? Val was looking a bit shifty when Finn was telling her about it, but surely she wouldn't have sent it because she has HIV herself and knows how hurtful other people can be. She might want to look out for Finn and protect him, but I can't imagine her doing that. I think Emma sent the text - she wants to interfere and meddle.
I can understand Emma and Ross's concerns and wanting to make sure Finn knows the precautions to take. I hope this doesn't come across as offensive, I apologise in advance if it does but I'm surprised that Finn is laid back in his attitude regarding starting a sexual relationship with Darren. I was expecting him to be more wary and nervous, and understanding his mum and Ross's concerns a bit more. Of course HIV can be treated and managed these days and it isn't a death sentence but it's still a disease, so I was expecting Finn to be more aware of the precautions he has to take.
So I can understand Emma and Ross's concern, but if either one of them sent that text, it was totally the wrong thing to do and the wrong way to go about looking out for Finn.