If I didn't know that I've just received a new car from you, I'd have to think that you wanted to cheat on me (or have an affair).

Sorry, 'wanted' is wrong here. '...that you'd cheat on me'.

donald: gut, aber man muss die Zeit etwas genauer einstellen:

"If I didn't know that I had just received a new car from you, I'd have to think that you were going to cheat on me" (oder, wie gesagt: ". . . have an affair.")

Ist aber ein sonderbarer Satz und Gedanke.

"If I didn't know that I had just gotten a new car from you, I'd have to think you'd cheat on me"

@Bob: the way this sentence is constructed, the "würdest" doesn't imply a future event, IMHO.

dude, that's a good point.