It's not okay, but there are cases where I personally would be more forgiving, having been like your ex gf before. I'm getting better, but it's a process. Namely, is this a new problem? Have these depressive episodes only recently appeared, meaning it is not only a scary situation, but a new and confusing one as well? Are they getting worse? Does she have a support network and the means to get help? Is the help not working? I know for me, personally, it took me several years to understand more exactly what what going on and begin to control lashing out.

Obviously, situations vary, and ultimately forgiveness and where to go from there is up to you. It does not give a free pass to be an asshole; however, if the affected person recognizes what's going on and is trying to fix it, I would personally give a bit more mercy. Just be aware that it can potentially take a long time for changes to occur, and just because they are getting better does not mean they won't fuck up occasionally.