To invest in Bitcoin, you don't have to go around saying, Let's invest in Bitcoin. It's totally a personal choice. Because investing in Bitcoin requires you to believe in it and have the courage to take risks. In the beginning, many did not have the courage to believe and take the risk of investing in Bitcoin, as you did at the time, and now regret it as the price has surpassed its previous record. But if Bitcoin didn't reach its new ATH and instead the price continued to decline from the price you saw, you might not have regretted it. Instead, you would regret ever thinking of investing in Bitcoin.
  However, I think you need to further educate yourself by gaining proper knowledge about Bitcoin before investing in it. Because you said, you told your brother to invest 50%–50%. But what you may not have known is that instead of buying 100% of your entire bitcoin, you can buy any amount, however small. And then, if you could have done your own research and gotten the right idea about Bitcoin, you wouldn't have needed to ask anyone; you would have taken the bold step to invest yourself and hold on. But we all seem to have some regrets about investing in Bitcoin.
You can still invest in Bitcoin if you want. But in this case, you have to test enough patience as well as have the courage to take risks. And of course, invest what you are prepared to lose.