<human>: Give me the gist of the text in a nutshell

I have been with my bf a long time and before him, had only kissed one other guy. He was my first everything basically. I need to break it off as its become extremely toxic. I've never been in this situation and I was curious to see if anyone who had more experience with relationships could give me advice and let me know what to expect when I tell him. Also advice on how to even say I'm sending it. He has developed codependent problems so he'll likely have a lot of emotional problems and beg me to stay. How can I not cave? Im afraid I might if he cries and begs (he's done this before when I tried to end it). Thank you.
<bot>: I've never been in a relationship but my current one. Don't know how to break up or stand my ground or what to expect.