So I've been on and off again since November with my ex. We originally split up when she gave me an ultimatum saying I either wanted a baby with her or I left (we had been together for 9 months). Anyway during our on off time we had both been going on dating sites etc and talking to other people. Whenever we were on, I wouldn't talk to anyone and when we were off I would. She would talk to them all the time regardless.
So a couple of weeks ago we decided to be serious and try again, we saw each other a few times and she was being suspicious with her phone. She always kept it face down and took it everywhere with her, texting on the toilet and when I went to the toilet etc. Though to be honest she's always done stuff like that, she's always acted suspicious with it and she's always been talking to other guys and I was fine with that when we were together as I trusted her.
Last night she stayed over and she was being really suspicious with it so stupidly I decided to look at it. She had archived messages in whatsapp and I discovered that not only whilst we were trying seriously but whilst she was with me she had been flirting with other men and I mean like sexual innuendos, calling them babe (which is a big deal to her), saying she loves them (which she wouldn't say to me). I know I was wrong for looking at it, I kind of tried to justify it to myself that she had looked at my messages once in the past (finding nothing bad) so I should be able to do it back to her. I know that wasn't right but I still feel what she had done was bad.

Anyway our whole relationship and on/off part she has treated me fairly badly, not just with this but other stuff too. She's a narcissist and blames me for everything. She blamed me for her flirting with several other men last night and for lying to me about it. Everything always comes back to me being blamed which I discovered a couple of weeks ago is a classic narcissistic trait.

After being with her for a few months in our relationship I started getting really down because everytime I was upset about something and told her she would blame me somehow or say I was being stupid or jealous. It got so bad that I got a lot of anxiety and rather than confront about things I would bottle it up. Since about 6 months in with her and to this day, the day after we have ended it for good, I've been having suicidal thoughts. Like I've not actively thought about trying to kill myself, these thoughts just pop into my mind. I'll be thinking of something and suddenly I'll just think about jumping out of the window or handing myself or jumping off a bridge or something.
It's not like in past where I've felt depressed and thought about how I'd do it. These thoughts I can't control, they just appear.

My question I guess is do you think this is just from my toxic relationship? Is it likely now it's over that they will disappear as long as I push through and get over her? Does meditation help get rid of these? I've been trying to meditate and it helps a little but it doesn't seem to be helping with these thoughts so far. Do I need to see a doctor?