with himself / by himself
Tom estaba hablando consigo mismo.
Tom was talking to himself.
No hay lugar para el odio en un corazón que quiere estar en paz consigo mismo.
There is no room for hatred in a heart that wants to be at peace with itself.
Tom parece estar bastante satisfecho consigo mismo.
Tom seems to be quite pleased with himself.
No es nada exigente consigo mismo.
He isn't demanding of himself at all.
Es poco exigente consigo mismo.
He is not very demanding of himself.
Así que es capaz de ser irónico consigo mismo también.
So he’s capable of being ironic about himself too.
— Fresas salvajes (1957)
No sea tan duro consigo mismo, todos cometemos errores a veces.
Don't be so hard on yourself, we all make mistakes sometimes.
He talked to himself.