Any advice on how to break up?

For context, my current partner is clinically depressed. We have to break up, it’s the end of the road for us. I just think and over think and I’m incredibly scared and overwhelmed with the fact that they won’t handle the news well and might self harm. I can’t live with that but I can’t come to terms with the fact that they cheated on me. I feel stuck though the answer is very obvious for me. I don’t want revenge or want any harm to come to them. In a perfect world for me, they would understand and we would split amicably. Once we were both ready and had money saved to separate comfortably. I know this person pretty well and know that this scenario of mine would never come true. I’m assuming they’ll be either Combative or cry but either way, will make it difficult.