@Anonymumm
OK first of all, stop with this 'he is very handsome and you would never put us together!' like you think you're a flippin' moose. 
He is with you coz he fancies you, he loves you, he WANTS you. Not some airheaded little flirty so-called friend of yours. And I bet she isn't as amazingly pretty as you think, and you are not as unappealing as you think.
I have had women in the past flirting with MY husband (especially at the school gate hometime pickup!) blatantly flirting, giggling, flicking their hair, and fluttering their eyelashes, and even slapping him 'playfully...'
One time, one 'mum' asked DH for coffee after he dropped our kids OFF at 9am- ish. (He didn't go!) I worked days - 3 days one week, 4 the next, and he worked night shifts at the time.
I know all this coz firstly, he told me, secondly, I witnessed it myself, on a few occasions where I finished early and got to the school 2-3 minutes before the kids came out, and I also saw the women doing it in front of me, whilst looking down their nose at me and ignoring me.
One time, a woman was being massively flirty with my husband, and I saw her (through the railings when I was walking through the car park,) and when she saw me, her face dropped. She looked SO disappointed that I had turned up, gave me a death stare, and continued to talk to DH, whilst completely ignoring me, and turning away from me like I wasn't even there. I said to DH after, 'did you SEE that? how she completely ignored me?!'
He said 'yeah I did actually!' And it was then that I told him how this kind of thing was pissing me off now.
I asked him how he would feel if the roles were reversed, and it was the dads at the school gate always chatting me up! And asking me for coffee a their house, (with only him and me there!) He said he would hate it. After that DH was polite, but didn't engage in lengthy conversations with the school gate mums... He just said 'hi' and moved on.
Upshot is though, that he didn't 'go off' with any of them, cos he loved me (loves me,) and was not interested.
You friend is out of order though, flirting with your husband. BAD girl code!!!
I would be ghosting her tbh. She clearly fancies him, and even though he is not interested in HER, that does not extinguish her flirting with your DH.
I don't think your husband (and other men) realise how hurtful and upsetting it is when women flirt with them, (and they are very friendly - and even a bit flirty back!) Coz if THEY are too friendly with the women, the women get the impression they fancy them, when they are often just being friendly.....
As I said, most men - if not ALL men - would not like it if the roles were reversed, and some mate of his kept flirting with you.