I think that maybe it is something only time can tell. If he's already made his investment then just wait and show him the returns. If he is too salty about it, he broke investing rule number 1 and 2;
- Do not invest any money that you are not prepared to lose in its entirety.
- Do not invest any money based on emotions, and don't let emotions control your trades.
I was considering paying him back, but it might be a better idea just to wait it out, tbh if it works out as I plan, steem day trading, and steem posting should both be generating massive returns shortly.