Indecisiveness between relationships

I broke up with my most recent boyfriend because I discovered I still had feelings for my ex, now that we have broke up in beginning to have feelings that I am regretting the decision and have been very upset about the break. My most recent boyfriend would take me back however I have now started talking to my ex again and I am scared that I have got his hopes up and I hurt him again. I need advice on what to do in this situation.