I THINK I AM CHEATING ! PLS HELP

so I broke up with my ex-boyfriend of two years because I was slowly losing feelings and I thought he was cheating again since I lurked on his snapchat and was talking so many other girls. So I broke it off. Then, I started catching feelings for my best friend and we're together now but I found out he smoked weed on the weekend and he told me he won't do it ever again. But my view of him has changed. He gives me a lot of affection and love, treats me well, but there's just no chemistry. I can't intellectually connect with him but with my ex-boyfriend I can. My ex isn't as affectionate as my best friend though. So it's kind of hard. Now my ex-boyfriend wants another chance and we talked and it was a misunderstanding. He wants to work things out again. And I just don't know what to do anymore. Pls someone give my advice.