Why would a man spend more time with his female friend then his girlfriend?

That could mean a lot of things, if their long time friends then there isn't much to worry about (Their most likely just close, might even think of one an other as brother and sister) Now if it's a newer female friend then there could be something going on there, it depends on body language or how they talk to each other. It could be something where they both have a certain hobby or something they both enjoy talking about. Now if there's something obvious going on there one shouldn't be afraid to call him out or ask subtle questions about it. Don't get to caught up on it, and don't be to pushy or clingy. Most guys don't like that, but remember its not bad to ask him about these things even if it's hard bring it up slowly. If he reacts bad to the question there could be something going on there. And dont think it's to clingy to ask him about it, he should know that if his girl friend gets worried about him being with another girl it's cuz she cares and other wise his girlfriend is likely thinking about somebody else.