Young man trying to decide if he should shed body (die) and put consciousness in massive simulation or stay out in the rapidly depopulating "real" world

This book has made a huge impact me and I remember it weekly but have never been able to find it again. Help me reddit!

In the book this guy is about to turn 18 or 19 (?) The age where he can decide if he wants to go in the simulation permanently (i.e) have physical body separated and killed. His parents are already in the simulation and he can visit them for short periods.

On the outside there is a cult/rebellion movement to stay in the "real" world because the digital world is too perfect and fake. The Boy has a childhood friend(?) Someone he knows in that group. He has a Guardian/best friend which is this gigantic construct that has three consciousnesses inside of it sharing one body. Two are male and one is female and they like sharing the body but can't go into the sim because of how they were created. There is a scene I vividly remember where the young man is watching a train or transport he knows is full of the Dead bodies of people who went into the sim.

I read the book in high-school or younger which was In the late 1990s and it was at the public library so it was printed either early nineties to eighties not sure if it could be earlier. The word internet wasn't used in the book. Can't remember the cover at all so it was probably very minimalist.