to start having doubts about a decision you have made
empezar a dudar sobre una decisión que has tomado (empezar a dudar sobre una desicion que has tomado)
"I'm having second thoughts about buying such an expensive car."
"Estoy teniendo segundas dudas sobre comprar un coche tan caro." (estoy teniendo **segundas dudas** sobre comprar un coche tan caro)
You can count on my support.
to begin a process that leads to a result
completely under someone's control
to fall deeply in love
to say something embarrassing or inappropriate
To do what you promised to do.