* "Je pense à toi tout le temps" means "I think about you all the time".
* "Comprend plus rien" is a bit confusing. It could be a shortened form of "Je ne comprends plus rien" which means "I don't understand anything anymore."
The most likely interpretation of the entire phrase, taking into account the grammatical errors, is:
"I think about you all the time, I don't understand anything anymore."
This suggests a state of confusion or disorientation, likely caused by the intense feelings of love or longing for the person they're thinking about.