Pensé que él fue contigo.
pensé que usted me amó
you say "tartamudear" I thought it was "tartamudez"
Pensé que tenías clases de español.
Pense que era otra persona.
pensaba que no sabrias (with an accent over the 'I' in sabrias)
Pensé que tu novia es china.
Asi que si yo le escribo esta carta.
Translation: He estado pensando escribirte. However, that sounds a little odd in Spanish. You may wish to say "I have thought of writing you" which is "He pensado escribirte".
the spanish thought of the aztecs as slaves
Gods.
They thought that the Spanish were gods incarnate.
Sister in law in Spanish is cunada.