Back with an Ex. Help

I have been seeing someone for a little bit and he asked me to become offical which I said yes. However the other day, I saw on his social media he was messaging other girls on snap. However, this was two/ three weeks before he asked me to be his girlfriend. When I saw this I freaked and dumped him and told my best friend. I decided to meet with him since I had to give him back his things and long story short, I decided to give him one more chance since to be honest 2/3 weeks before he asked me to be his girlfriend I was talking to other men. So who am I to get mad when I was doing the same thing. Technically we were not offical and I didn’t see anything recent of him talking to someone while we have been offical.

My best friend is now mad at me and sent me a whole message saying that it’s still cheating even if we weren’t official and he will do it again. Am I wrong for giving him another chance?