Does it sound like he's lying?

A guy who I've been friends with benefits for eight months recently let his friend of 10 years and her kid move in with him. He said there is nothing going on between them. He told me he's trying to help her because she's having a difficult time. He told me she doesn't have a license or a car. I told him that he likes her enough to let her move in with him. So maybe he should just be with her and he said he doesn't want to. I also asked her if they were in a relationship and she said they aren't together.

Then he was complaining about the living situation with her. The last time I saw him she texted him and he rolled his eyes. Saying that she was going off on him about eating some of her food. And that one minute they are ok and then the next she flips on him. He said he shouldn't have to feel stressed about living his in own house. And that everyone he asked about letting her move in with him told him not to do it.

I just don't want to have sex with him if he's in a relationship with her. And I told him I did not want to come in between them if they were together. And this is when he said they weren't together.

But does this really sound believable? I have always been told that men and women can't only be friends. Because one person usually tries to be with the other person. And every time I've ever tried to be just friends with a guy (unless he was gay) he always hit on me or wanted sex.