I started off thinking that this is a laughable question, but i think that is only because I am considering the question from the perspective of my own relationship. I probably have more male friends than DH does female friends, but we both have a number of friends and close colleagues of the opposite sex. Although it is true that we both tend to see friends (both male and female) in a larger group, that is not always the case and i am sure neither of us would think anything of the other meeting a friend (of either gender) one-on one. If I was out with one of my male friends (mainly old uni friends or people who have been colleagues for years), the idea that DH might have reason to be worried is just ridiculous, and I of course extend him the same level of trust that i would expect him to have in me in equivalent circumstances.
On the other hand, a NEW non-colleague female friend i would wonder about, largely because i am not sure how he would meet such a person. Going on holiday i would also find strange, because he gets less annual leave than me and we tend to go on holiday as a family. I would feel the same about a holiday, though, whether it is a male or female friend. Even then, if it is something he really wanted to do that I did not want to do (or was not ideal for the kids etc), I would not have a problem with him going with friends. He has been to watch England play rugby overseas, for example. That has been with male friends as it happens, but i don't think i would have minded if one of his female friends was included in the group.
I think the above represents a "normal" relationship.
On the other hand, I then thought of a lovely friend of mine and I can imagine her asking the above question and (wrongly) taking a lot of comfort that she has nothing to worry about in her relationship based on the general thrust of the response to this thread that it is of course fine for husbands to spend time with female friends. Her H recently gave up work (although they have kept an au pair) and he spends a lot of time going out to lunch and dinner and clubbing with new female friends, and is now starting to arrange holidays etc with them. There is more i could share but in his case, the way he behaves is absolutely not something i would tolerate, but my friend is sadly in denial.If someone picked her up on the way her H acts with these friends, I can imagine her posting precisely the above question and taking a lot of reassurance form the responses that her H's behaviour is really nothing to worry about, When i suspect it is.
Hence, without knowing the relationship in question i am slightly loathe to make categoric statements.