Am I over reacting?

My ex and I got into a fight and he told me to OD just like my uncles had the week previously. I started crying. My "best friend" was there just watching, silently. She later DM'd me "sorry" and I asked her why she did nothing she simply, replied "because I don't want to get involved. If I get involved, there's no chance we'll be friends" (her and my ex.) Me and this girl have known him for a year and a half now, but we've known each other for 7 years. I just feel like she should have stuck up for me if she was a real friend. Now I don't want to talk to her. And she makes no effort to talk to me.

So, do you think I shouldn't have expected that from someone and I'm over reacting or do you think what she did just proved she wasn't a real friend?