"me and my size nines"

Well, his 'size nines' are his shoes, but you have not supplied enough context to explain why he mentions them. Nine is a rather average shoe size for adult males.

Thank you for your answer.

There's no other clue in the dialogue that could help to understand this phrase. I don't think she's talking about her shoes. I suppose she's talking about her problems, but I'm not sure.

Well, there certainly must be more context.

Size nine would be a large size for a woman. I have no idea if this has relevance. There's no idiom here, though. Just facts.

Has the woman said anything to offend someone, or anything she might now regret? If I had to guess I'd say she was referring to having "put her foot in her mouth."

http://www.answers.com/topic/foot-in-mouth-disease-album

Oh! Good guess!

I wear a size 9 myself, and am a little sensitive about it. Particularly as it's the size worn by Clementine, the miner's fabled daughter, for whom "packing boxes without topses" served as sandals.

The person who asks 'How could You?' is answered by him referring to his size nines. (English shoe size)

In Englsh we have a saying that if you do something wrong you 'Put your foot in it' like stepping into a pool of water or other substance.

So the person answering is saying that he has done something wrong by doing or saying something he shouldn't have and then the other pers

It means that you have said something clumsily, or not as gently as you could have done.

It relates to uk foot size where size nine was large for men and especially women. Sizes are now bigger! But it means "my larger than normal feet have not been treading as carefully as I would like; I have made a clumsy error in what I said".

Compare: "Putting your foot in it".

In this case size-nine are his shoes. In "He Died with his eyes open", chapter 10, by Derek Raymond (a wonderful novel) you can find this idiom meaning a cop.