Even if there's an agreement, there's still a risk of losing your trust.
If you can invest on your own much better, but if you really trust your close friend and you believe on his knowledge about trading and investing, then why not maybe you can just invest small portion of your extra profit so you will not miss the fun with your friends. Personally, I prefer to invest on my own privately.
I quite agree with your opinion. Wherein is it wiser for us to manage our own investments without having to do it with other people or trusting other people for our assets. I have seen many cases where they lost most of their money because they trusted their investment to be managed by someone else.
So in this case, every investment that we make might be better managed by ourselves, even though the profit we get is smaller because of the small capital, but in terms of security, of course it is very prioritized. Besides that, there is no feeling of anxiety or worry about our money or when we need it, we can take it instantly without having to wait. Apart from that, in the current era, it may be difficult for us to find a word of honesty from someone or our friends or new people we know, so that it will have a negative effect later if one of them makes a mistake which can have a big impact on the course of the investment they are making. So I don't think that's a very good thing to do and might cause all misunderstandings to occur later.