I think the only choices not mentioned are the first scene after playing video games with him, in that scene you have to choose to LOOSE-WIN-LOOSE-WIN. That will unlock a scene of jerking of together. If you do all that he should be present at the fishing trip. If you have the relationship with the blonde girl you choose him to sit in the back of the truck (otherwise it happens automatically). During the car ride you need to tell him "I don't mind". I don't think choosing him at the lake is necessary but you may do it to make sure. Finally choose him to go to the cave with you. The rest should develop from there.
I also recommend either using JokerLeader's walkthrough for help and/or downloading the walkthrough from the creators patreon, but that one is a bit hard to navigate, make sure you can read pdf files well.