My son is the world to me, when I saw that my ex didn't factor in our child when he was acting like a fool, crying or shouting in front of him, ( as in our son was in the other room and I would tell him this wasn't the time, he didn't understand that) I had to end it, I tried for our ds because he could be a good df at time.
The lying and cheating, when he would leave for a week or two were just extras but it was my ds happiest.
For the first month I spent a lot of time just playing with him, chilling in front of the tv, going for walks together. Taking time to relax and just play. Obviously I had other things to do, but I really didn't care about cleaning etc cause I needed to maintain good care for myself and ds.
Since then I have focused on my ds, it sounds simple but truly there isn't anything more important, I was always the main parent cause my ex works a 70 hour week, but instead of thinking I should be doing this and that like others my age, I think what does he want to do today.
I'm just extremely lucky I did it in January and didn't have to spend lockdown with him. I don't know how your dp with take it, mine harassed me for 2 weeks, and then disappeared completely. Only to resurface for some clothes, not ds.
Also TikTok helped a lot, so many other have the same feeling as me.