<human>: Can you give me the gist of the text in a nutshell?

My SO has been extremely depressed lately, and a large portion of that can be related to his mother and their relationship. She is far too controlling and quick to anger. A few weeks ago they had a huge falling out. Now they're mending their relationship. She thinks that with all the things he has told me that I must hate her. I don't, I don't think much of her parenting skills from what I've heard, but I also don't know the full story. I prefer to take a rather subjective view on issues I'm not directly involved in, so I really don't have any changed feelings towards her. 
However, I have never been completely comfortable around her. I've done some pretty questionable things in my past, and I get a very judgmental vibe from her. So naturally I'm a little unsettled by her, but nothing that would keep me from being polite and friendly. I would just be really uncomfortable being alone with her as I feel I have to put on more of an act than I am comfortable with.
My SO says that she wants to go to lunch with me to "clear the air", I told him I was not comfortable with that. He got quite clearly upset and told me that he wants me to try and help him repair his relationship with his mother. I'm all for supporting him through this, but I also see this as just being an absolutely terrible idea, if he came with it would be fine. But her and I alone seems far far too much. I don't want to upset both of them, but I also don't want to agree to this and then screw everything up. Am I wrong to outright deny to this? If not, how do I have my SO see that?
<bot>: Boyfriend had issues with his mother, they're fixing it, she thinks I must hate her, wants to go on a one-on-one lunch with me, I don't really want to.