I sort of agree with Hora here (Gulp)…
You can’t be utterly certain of your loved ones behaviour, however the more you know them the better you get at being able to understand/predict and hopefully trust them…
If My missus had texted me two months into our relationship to tell me she was out at a nice restaurant with another fella, I’d have taken that as an indicator that we were on shaky ground…
There’s some truth in this in my experience. There’s always that one guy orbiting around who you just know desperately wants to bang her. Of course you can’t say this. You must ignore the elephant in the room and respect her platonic friendship, which is fine, all in the game etc… but whenever you have an argument, she’ll always end up round at his (I don’t think anything’s going on, just that he’s the only one that would drop everything/drive 200 miles to pick her up etc, and maybe… just maybe, a little part of her might think it’ll wind you up). When you suggest that she might at least give the poor besotted backed-up fool a handjob, you’re suddenly the villain again…
I did have one Ex, who started spending lots of time with a platonic male friend to try and get me jealous and crash the relationship, after about a year, I didn’t bite and she ended up having to be honest and just say she’d had enough, which was fair enough…
It’s a tactic either gender can use; you break no spoken or implied promise to be faithful to the other party, but sail as close as you can to that boundary in order to make the other party seem controlling/jealous/unreasonable, cause an argument or two and then end it because they’re a bit mental… The OP knew this when he took his platonic female friend out for a curry and a whine about his current GF…
Just crack on and put the poor girl out of her misery, do it via text if you like: