I mostly want back to the point I was or since I think I made a mistake and I don't know if a mistake ruins the whole relationship.
I have an old save that I found, but I don't have the bathroom scene for example I believe.
There is often leeway for mistakes, though some individual mistakes can ruin a path on their own. The bathroom lewd is not mandatory for Dalia's path. If you got to the end of 0.4 with her path intact, you're probably fine.
If you want to be 100% safe, you should fully replay the game alongside a walkthrough because future consequences & affection point thresholds are still unknowable. Some people fully replay Eternum with each new update!