Ex's old best friend asked me out?? Not to mention he had a thing with another old friend of mine...?

So there's this cute kid about a town away from me. I met him when I facetimed an old friend of mine back in July and them two had great chemistry but apparently my friend blocked him after they hung out and never spoke to him again and her and I are no longer close enough to where I can ask her what went wrong and she's repeatedly slandered my name. Now the cute kid slid into my DM's about a month later (August) but I politely declined being with my now ex at the time. You see my ex and him were good buddies before I met any of them. Now neither my ex nor my old friend speak to this cute kid so it wouldn't kill me to leap forward with him but there's a slight problem. I am not completely over my ex (we broke up late October for various reasons) & the old friend of mine went to elementary with my ex and her new bestfriend is trying to hook up with him. My ex promised me he wouldn't **** around with those two girls (The old friend and her new bestie) I have a feeling if I continue forward with cute kid then my ex will hookup with the old friend's bestie. Shouldn't be my problem right? Always move forward never back. But again I am not COMPLETELY over hime yet.. any thoughts?