Like others have said, I don't think it has anything to do with being Greek or non-Greek, it's all about maturity and trust...I mean, if a guy has a problem with you going to a function with a male friend or without him around, that has zero to do with him being non-Greek, and everything to do with him not trusting you and perhaps being a bit on the controlling side, and people like that come in both Greek and non-Greek versions.
That's not someone I'd want to be with either way.