OP he has twisted you all up into knots. Can you see that?
So you lied - in self-defence, because you knew that he would use this against you forever, even though you did absolutely nothing wrong by seeing other people while you weren't together. This is NOT a normal or reasonable thing for him to be upset about, which is why you haven't done anything wrong.
You actually had a perfectly reasonable self-protective instinct in lying. Because it's not something that any normal partner would expect of you in the first place.
He keeps saying that you "haven't taken accountability" because his thinking is so screwed up that he is not being rational, he will never be rational about this. It doesn't matter what you did or didn't do. He would have come up with some imagined crime and berated you for it anyway. And he is unlikely ever to stop.
This man is dangerously controlling and possessive. Men who kill their partners or former partners often display this kind of irrational level of possessiveness. I actually think you are at extreme risk. Please talk to everybody you can in real life about this, and consider contacting Women's Aid, or a local coercive control support unit, for some advice and targeted support.
See this video/article about murder: https://news.sky.com/story/off-limits-who-is-most-likely-to-kill-you-11734990
And download this free PDF of the most life-changing book: https://www.docdroid.net/2fZmz40/why-does-he-do-that-pdf
And here is a selection of ways you can get into contact with women's aid. You don't need to give your name and they won't report to the police. There may be an option for example of counselling. It is totally your choice what you do, and nobody will force you to do anything. https://www.womensaid.org.uk/information-support/
Please be cautious about your internet history if you think your partner might realise that you are looking at these resources.