Sorry, I probably have said enough already

....but I can't help wondering how he would feel if it was
you seeing another bloke under these circumstances ....????
Another way to look at is, does the OP have some perfectly innocent male friends? I am sure that she must do.
I would certainly be very worried if my husband started telling me which men I could and couldn't speak to. It probably wouldn't be the fact that I couldn't speak to someone that would bother me, much more the jealousy, dis-trust and control.
hmmm ......and then to cap it all, deliberately & quite blatently arranging to see them
again when you are not around.........sorry, I think that is NOT the mark of a sensitive, caring bloke.........please don't let him manipulate you into thinking
you are being unreasonable.
But men are often not "sensitive" - it doesn't mean that they don't care, it is just that they don't think sometimes (ok, sometimes quite often...!

). I think that this is another thing that shows that this ISN'T anything dodgy: yes ok the OP's fiance was a complete twit and arranged a second meeting, BUT he told the OP about it. He is being completely honest because he has nothing to hide and doesn't think that there is anything remotely dodgy about it in his mind (about either meeting or about the whole thing...). Yes, he is being insensitive/ignorant, but his actions/words are also saying "there is nothing to hide and I am not doing anything wrong".
Only the OP knows her fiance, but good marriages work on trust and partnership. It sounds as though the OP's fiance is trustworthy, the OP just needs to work with that: i.e. get this new friendship where it belongs (in the context of their engagement/marriage) and not to start World War Three (which will cause resentment etc).
As I said, this doesn't mean "put up with things how they currently are", BUT work with him to allow him this friendship in a much more suitable way.
Like any relationship, you can get a lot more out of co-operation and gentle manipulation than by fighting an all out war
Alice