I wouldn't say that, Alex got blackmailed and we can't forget that he was still a teen at the time, came from nothing (felt completely powerless) and probably panicked to the point where he didn't think stuff through, especially seeing that Nathan was ambushed. He just wanted to protect Nathan and was scared. Those circumstances don't lead to the best decisions. I'd say he held the pain of feeling pressured to push Nathan away for a long while and that makes the angst somewhat believable

Miscommunication is always the plot device used to drive the main characters apart and it can 100% happen in real life but I personally feel like the execution and set up for why the miscommunication happened was very weak. The lie was a million times worse than the truth and it truly did not make any logical sense for the lie to be told. I can see where they tried to set it up but it was a total swing n a miss for me.