I had a similar thing happen, made a startup when I was 18 and incredibly dumb. Half my money and half an investors.

Ended up having to wind it down because it was a stupid idea and I realised quite quickly after spending money on it. Was a small amount of money but a lot for me. Luckily the investor never asked for money back.

Wound down my second one too but lost no money.

Then came into some money through a software sale about 7 years later, and offered to pay the first investor their full investment back, which was about half the money from the software sale (my only sale ever).

They really appreciated it but declined and instead said no, they want to invest in me AGAIN in the next one.

Felt really nice to have someone believe in you so much they would open themselves up to money risk again rather than take their initial investment back