Lilybell, I agree with
Suzanne when she suggests your a partner is consumed with his concern for his daughter. Over the phone he told you it has been a stressful time, and when autistics are under stress we tend to have a one track mind. That would also explain his talking to another person (who happens to be a woman) about his daughter: that is what he needs to talk about because he is stressed. He needs to work through it, even if he isn't conscious of that need.
And the mixing up names... I do that, too. I mix up my two kids, I mix up the kids and the pets, I mix up my son and my brother, or my husband and my son, and so on. It depends who, or what, is on my mind... Whatever it is,
that is the thing that will usually emerge from my mouth. It makes for very embarrassing situations!
Some things fairly common among autistics are honesty, trustworthiness and faithfulness. I would be
extremely surprised if your partner were cheating on you. It's understandable that you are anxious about that, but I don't think you need to worry. He went away to spend time with his ill daughter. When you became suspicious it sounds like he quickly became exasperated. He has spent days totally consumed by his stress about his daughter's illness and suddenly, completely out of the blue, there is an implication that he has been away doing something else far less honourable.
Please, don't worry too much. I used to find it weird that my husband (not sure if NT or autistic) would go to bed without a word, and I'm the Aspie! But I realised it didn't mean he had stopped loving me or anything. It's just a comfort thing. He feels comfortable and safe enough with me to not feel the need to go through all the niceties. When viewed in a different light, it can be a good thing.
If you and your partner have issues with communication, I recommend working on it together. Tell each other what you like and need and be prepared to be flexible, too.