That is a correct sentence. It may or may not be saying what you want it to say, but it is correctly constructed.
“Even though” means the same thing as “despite the fact that.” It is used to show contradiction between two parts of the sentence. Let’s try a simpler sentence:
Even though I like ice cream, I couldn’t eat my desert.
The fact that you like ice cream would normally mean that you would want to eat it. Not eating ice cream is the opposite of what you would expect from someone who likes ice cream.
Getting back to your original sentence:
Even though my friend seemed to enjoy the movie, I thought that it would never come to an end.
This is expressing the idea that you would normally expect to like a movie that your friend enjoys, but in this instance you were bored with it.
So that implies causation. If you say “A so that B” that means that A enables B. For example:
I gave my life so that others might live.
This implies that giving your life allowed others to live.
Because implies motivation or causation. “A because B” means that B causes A. For example:
I eat because I am hungry.
Being hungry is the reason you eat.