Regrets are there because you've learned. Learnings won't mean anything if you won't reflect and apply it. You saw how big the potential is for Bitcoin's market value; are you investing now? It is easy to tell other people to invest but if we don't have the courage to do so, simply because we saw the price on a decline at the moment, then what's the point? Take the risk if you want to achieve something or gain profit. If you know how to properly manage the risk then at least loss won't hurt that much. Taking the risk is different from being reckless, keep this in mind. It is Bitcoin we are talking about and we all know how capable this digital currency is, to be bigger in the future. Erase the idea of easy money scheme 'coz there's no such thing.
If you invest your 100% of what would have been your half of the capital, you'll get the exact sameprodit as if you both had invested and you shared the profit. You could have easily bought with the amount you had and held for as long as you would have planned to.
Secondly you never compel someone else to invest in anything. You're putting unnecessary risk on yourself as you'll take the blame if that investment goes south. Only give them information that can help them make up their mind on their own.
Thirdly, you still have the opportunity to take a risk now. Bitcoin still has a way to go in this bull run.
Waiting for a lower market value could still be considered. People are just being hasty of the market price simply because halving took place and yet no significant changes could be seen other than the temporary dump.