I don't think the issue is snapchat at all.

I think the issue is insecurity with your gf and this other bi/gay guy.

You have no reason to believe she's been unfaithful to you from the sounds of things?

You did say way earlier on in this thread that she said that she told you that she's reopening snapchat.

As the saying goes, "don't borrow trouble".

As to whether or not she should legitimately have snapchat or not, I don't know. It's going to be a contentious issue, if, she is using it for the purpose of communicating with her family.