I find that with LinkedIn networking and sending people messages it's important to think that you don't really lose anything if they ignore you so it's always better to shoot your shot so to speak and see what happens. When I was working on various startup projects, I always found that in terms of keeping further contact it's always best to kind of have specific asks in mind. Often the initial contact was quite short but if you're doing something interesting or relevant and you're a young person people tend to want to help! In terms of templates, I didn't use those I just tried to make sure the message seems personal and I took the time to understand the other person and keep it as short and to the point as possible.

I've lost a bunch of friends over the years during university as well as after - I think it's really sad but also an unfortunate part of life, and isn't talked about enough as you said. I am often wondering if it's a problem with me but find it unhelpful in terms of maintaining a positive outlook on things. I hope you get to meet or re-connect with some great people soon :)

This was beautifully written!