Can I Get Some Help About A False Harassment Charge?

I will give you the short version. I loaned a friend some money. Wrote a check which "noted" on the memo line that the loan was for 1 month. The friend fell into hard times and started bringing me partial payments towards the loan. Recently I contacted the friend and asked if he could complete payment of the loan because I am in need. He told me he would have the money by "Friday". Of course, has come and gone and I did not receive payment. I contacted the friend on Friday by phone and text and he would not respond nor answer my call. Contacted again on Saturday and Sunday and no reply or answer. In one text I explained that I really needed the money and didn't want to ruin our friendship. Therefore, my next step was sending a certified letter to his home requesting payment in full within 15 days or a phone call. Of course when he received the letter he contacted me screaming that it was not a loan and I was just helping him out and said if I needed to I could take him to court because I had no proof. I mentioned I had a copy of the check which would be proof enough. We hung up and two minutes later he called my cell, which I didn't answer and l left a message indicating he would file harassment charges if I contacted him again. The next day I get a phone call from the police indicating they were giving me a warning for harassment due to the correspondence I sent requesting payment of a loan. I could believe it. Anyway, I am going to file a complaint with Magistrate Court for repayment but I know he is going to retaliate by filing a false harassment charge. What are my options? If he files an harassment charge, will the police arrest me on his word without any evidence? I am worried about them showing up at my job and losing my job because of this. I would never have expected this from this person. I guess money does cause people to do crazy things. I can't believe a debt collection letter would be grounds for a harassment claim. If that is the case, can we file harassment charges against all of our creditors and have the police contact them?