Man, I am really sorry you went through this. While this guy may have been your best friend, it sounds like he has a lot of underlying issues that you didn't know about, and that is what caused him to have a bad trip. I really don't think any of this is your fault, and the people who are saying it is clearly don't have a real grasp on the situation, or what it's like to have a bad trip. For whatever reason, he didn't have the mental strength to wade through the more difficult parts of tripping, like fully fleshing out thoughts and sentences. Maybe its because he is confused about his sexuality, and subjects like that can be really difficult to try to reason your way through in that state of mind.
That said, I would try your best to let this experience stand alone in your mind, and don't completely write off tripping with other people in the future, as this is not how is usually goes down. This guy was not ready for acid, and you weren't ready to deal with that, because you thought he was ready. I think it's crucial that you take this as a learning experience. Positivity and mental strength are the two most crucial ideas to have in your mind going into a trip, and when you see someone on the verge of having a bad time you have to calmly impart this onto them. If someone is babbling and making no sense, tell them that they need to try harder to complete their thoughts and be mentally strong and positive. The world is still normal and you're just on drugs, it'll be over in a few hours. Say it with a smile. You getting worried and paranoid likely only made things worse for him, and yes you are right, taking him outside was a bad idea. Try not to feel guilty about that, at that point you were just trying to do damage control and you didn't know what you were getting into. Now you are better equipped to deal with something like this in the future. It sucks to lose a friendship, but clearly your friend was not on the same page with you as much as you'd previously thought. He's probably blaming you for what happened because he's not in a place where it's possible for him to take responsibility for his actions, and that isn't your fault either.
Soldier on, friend. This is a beautiful and extremely powerful substance that needs to be treated with great reverence and care. I can only hope you'll be able to experience the beauty, peace, love and light again, unclouded by the perspective of someone who wasn't ready to see it.