It’s probably fine OP, but just to be certain, years of reading the relationship board on here and living/learning from others teaches that affairs do happen in otherwise good marriages, because the normal stresses m/drudgery of midlife can leave people vulnerable to the respite of feeling the good addictive feelings that being fancied/fancying someone can bring. Sounds like you and your husband have good communication, so it’s important to talk about this and future proof yourselves.
Not to worry you but the below worst case scenario is classic territory for the beginning of “the script”
Search for it on the relationship board www.mumsnet.com/Talk/relationships/2558126-The-Cheating-Mans-Script
Worse case scenario. The girl has a crush on your husband and is drunkenly texting him song lyrics.
Husband is unaware up till this point.
Now husband is aware and despite being a decent guy in a good marriage, is flattered that a young girl could fancy him. Thinks about it despite himself.
Despite relationship being fine, only normal midlife stressors in your husbands life ( normal work/life stress, worries about money, worries about ageing , worries about Brexit/corona) the thoughts about the idea of being fancied start to become a respite from this stress. Almost imperceptibly at first.
Then something changes in the way he interacts with this girl. He starts to see her differently.
A flirtation / emotional affair starts to develop, almost just in your husbands head at first. The feelings though that this gives makes him feel good and provides respite from life stress.
But it’s confusing too, as the feelings also make him feel guilty. Usually this makes someone stop. But sometimes...
And here’s the mind trick that people caught up in this sequence of events play in themselves almost accidentally (and when it gets dangerous) .... the guilt for having and enjoying these feelings develops, and instead of seeing it clearly and realising that it’s a response to shared normal stress in life , the person starts to blame their partner for the stress and the need to escape into emotions.
this point is where things get dangerous and an affair develops, justified in the adulterers head in that the marriage spouse was to blames for their behaviour.
That’s why for alit of people being cheated on it feels it comes out of nowhere and they feel gaslit, because the marriage genuinely was ok (albeit subject to normal life stress)
And why a lot of alduteres utterly fuck up their lives/marriages/families and are left feeling bewildered and almost having to double down on the new relationship, because they genuinely have to perform this mind trick on themselves to justify the falling of cards that happens once the situation starts to unfold.
It’s horrible to see it happen to people.
Best way to protect yourselves is to be aware of the scenario. Talk about it openly. Know that this happens and acknowledge vulnerabilities and stress.
All the best OP x
Best way to keep your marriage safe is to not ignore stress, to always talk about it either if you can’t solve it, to acknowledge and communicate clearly. And to be aware if this process and how it can happen.