Cheated on years ago

I have been dating my s/o for almost 7 years, I just found out he cheated on me years ago, we have a 3 year old & the cheating happened before my daughter was born. Idk how to feel about it since it’s been so long ago. Like he said he couldn’t fully cheat, his conscious beat him and he just stopped and left. Is it bad for me to stay? Do I leave? Like idk, in my head it happened so long ago that idk how to even react, i don’t even feel upset… idk if I’m still in shock?