So there are more reasons and I've come to know one of it personally.

As to why guys and girls can't just be good friends. Like why people don't believe in platonic friendship.
I of course disagree but.. you can't fight it when you good friend is your brother's best friend.
Difficult, tricky situation.
Especially if you're not close to your brother.

And I probably have to rethink some things such as hanging with guys alone. I think if it's a long-time good pal, it'd be fine like tom. But if new friend, plus late at night, probably not so good huh. It's difficult to think what's good or not, and I'm trying to put myself in the other position, i.e. if it were my husband would I be happy etc...?

This could be a habit from my old life. But.. made brand new, I want to reassess them, and cut them out, if it doesn't honour God.