Does anyone have advice on how to deal with a friend who is in a perpetual state of grumpy??

One of my best friends through high school dated two guys back to back long term. During that time, our relationship plummeted terribly. To the point where I nearly broke off our friendship altogether. She was constantly in a terrible mood. Constantly trying to one up me in aggressive and hurtful ways. It just wasn’t the type of friendship I wanted anymore. I cut back on our communication and such, but after the second break up she slowly came back to her normal self and mood. We quickly rekindled what we had before and it was great having my friend back.

Now she is in a relationship again, and has progressed to her grumpy and spiteful mood. Everything is negative when we speak and it seems like whenever she’s in a good mood, it’s in an attempt to make me feel bad about myself or my situation. I’ve been left wondering how this switch could happen so suddenly when things were back to normal between us. The only common denominator I can find is she’s acting like this only when she’s in a relationship.

I know I can’t do anything about the relationship aspect, but does anyone have advice for how I should handle her negative attitude, bad moods, and spiteful remarks to me?