WTBH, I know how upsetting you found the visit from the police, but they weren't there to slap the cuffs on you, they were investigating an allegation--as you would want them to do if you called to report something.
Sammy is right, the visit from the police is documentation. If she alleges anything else, that police report is gold. Her credibility as far as allegations against you is pretty well shot (unfortunately she probably damaged her credibility as far as any allegations against her b/f, too, should she decide to report anything involving him).
So I don't think you have anything to fear in terms of someone in authority believing lies against you. You're going to cooperate with any investigation involving CPS. And, incidentally, just because you don't hear from them directly or you don't see/hear of anything being done, doesn't mean they aren't doing anything. It's most common as a first step to investigate and offer any services that may help the home situation, unless the kids are in immediate danger. Their dad knows, too, so assume he is monitoring the situation.