Boys boys boys

So, I was dating a guy. Let's call him "A". Well me and A were dating for 9 months, and the last month one of my best friends and I (let's call him "J") reconnected. I was taking a trip to Washington DC, and J is stationed in Quantico, Virginia (he's in the Marines). Of course I wanted to meet up with him, we've been best friends for 2 years and I hadn't been able to see him prior. We met at a Starbucks and had about 2 1/2 hours to sit and talk. I realized the feelings I had for him in the past were real and I felt a serious connection with him. Previous to us meeting me and A were having serious relationship issues. I wasn't happy in the relationship at all anymore and now I don't understand why I let the relationship go past 3 months, when he ruined my winter formal night by being a jerk about driving me and a friend. Anyways, my mom even had noticed I wasn't excited like I used to be when he was able to come over. After returning from Washington DC, I broke things off with A. It was a crappy break up and he was obviously hurt. After the breakup, J and I were extremely flirty and we ended up exchanging nudes. (We still are flirty to this day and like each other a lot.) Now, my ex is trying to make it seem like I cheated on him. I didn't kiss J, nor send him nudes or be flirty while A and I were dating. We hugged before we said goodbye but that was it. I understand why he thinks I cheated, but I didn't, should I confront A about him posting things on Twitter about me cheating? Or should I leave it alone?