<human>: Could you distill the essence of the text into 1-3 sentences?

My friend (let's call her abby) has always been a negative slightly bitter person. However, slowly over the last few years this has spread onto her reactions to the things I tell her about my life and I'm sick of it.
The last straw for me yesterday was when I text abby that I'd been invited to an open evening for a job I have been desperate to get. The conversation went like this:
Me: I got invited to an information day for the job I was talking about.
Abby: that's really annoying 
Me: why? I'm really excited about it 
Abby: yeah but it's just a pre interview interview. What would you wear?

I know this may seem minor but a few weeks before this I was seeing someone I really liked (didn't work out but that isn't relevant here) a conversation with abby about it went like this:
Abby: are you seeing BF this weekend?
Me: no he's visiting his parents back home 
Abby: see if that was me I'd assume he was fucking his ex right now.

I'd never said anything to suggest he would cheat (he didn't and that's not why it ended) and she had never met him. It drags me down talking to her and I'm sick of being drained in every conversation. 
I'm not sure if I should address it with her to help her change or just walk away. I'm pretty much her only friend so I do feel a bit sorry for her.
Have you handled anything like this? Advice on what to do would be appreciated.
<bot>: friend gives dramatically negative responses to any/all updates about my life. I want to know if it would be best to help her fix this or walk away.