"I don't understand why things always go from perfect to weird with us" reflects frustration over the sudden change in their relationship. The speaker feels that their interactions shift from enjoyable to uncomfortable, highlighting a pattern of instability or misunderstanding between them.
"It's like we're incapable of normal human interaction" suggests a struggle to communicate or connect in a typical way. This sentiment expresses disappointment and confusion about why maintaining a smooth relationship seems so difficult for them, emphasizing the emotional distance or challenges faced.