in my opinion there's nothing inherently wrong with a guy friend if their relationship is innocent.
if they're friends because they've known each other forever, they have hobbies in common and get along, that's fine.
if she's constantly searching for new men to add to her harem, hang out with men who cannot possibly have anything to talk to her about (hardcore video gamers, sports nuts and construction workers when she's a fashionista who follows the kardashians), and they're not even good friends, that is obviously shady af and needs to be dealt with.
if she pretends to be oblivious that many of her guy friends want to **** her (unless she's like 16 or super sheltered and naive), if she intentionally leads on guys who want to **** her instead of making it 110% clear that they're just friends and she has a man, etc. that's bad.
when it comes to hanging out with guy friends, this is the most important part of the post: if the activity is an activity you could expect to get laid during/after, she shouldn't be doing it with other guys.
can she go out to coffee at noon with a guy? have you ever gotten laid at 12pm after a cup of coffee on a first date? probably not unless it was tinder or a craigslist ad. can she netflix n chill with a guy? of course not, that's the prime situation to have sex while sober. can she go out for drinks at midnight? of course not, why would you want a drunk guy to walk your drunk girlfriend home? sex is destined to occur. can she head to the local park/playground to play handball with a guy? sure why not? that's a perfectly normal activity and it's done in public parks with people around so no sex has any real chance of happening.
it sounds like your girl is banging this guy though OP considering that she's having secret meetings with him and going out with him for drinks