Anonymous wrote: It's your husband's job to nip this in the bud. He's married and shouldn't be flirting with vulnerable single women. Occasional casual flirting with your married friends is much different than single ones.
As an outgoing person who comes off as a flirt, I am glad to hear this. I am married, happily, to my partner of 20 years. I grew up with lots of brothers, cousins, friends of brothers and cousins, male sports team members, and neighbors, in a smaller Midwestern environment where ribbing and teasing was a big part of relationships between friends. I find that when I am around other people from similar backgrounds, our ribbing and teasing and comfort with that mode of interaction can come off as flirting; I also find that I am more outgoing and exuberant with people who are more loosened up, since that's how I grew up.
Which is all to say, OP, you have spoken with your husband and you have an understanding. He knows what cheating is and he is responsible for himself. If she is lapping up the attention, there's nothing you can do about her feelings or her end of it, as long as the attention he is giving is in the vein of his regular way of behaving. You can let him know that you don't want the dynamic between them to escalate, but you have to trust him to keep an eye on it. If you can't trust him like that, you do have something to be insecure about, unfortunately.