Look back on: think about something in your past. Reflect on. E.g. to look back on your childhood.
Constraint: a thing that limits or restricts something, or your freedom to do something. Restriction. E.g. constraints of time/money/space. Financial/economic/legal/political constraints. At last we could relax and talk without constraint.
Flattery: praise that is not sincere, especially in order to obtain something from somebody. Adulación. E.g. you're too intelligent to fall for his flattery.