I am 23 and torn between my ex and current girlfriend

I am 23 and have been dating this lady for about 8 years until June this year when we decided to call the relationship off. The main reason for the break-up was that I often flirted with her friend and this apparently hurt and made her very angry to the point of hurling insults at me and my family. She even had her sister tell me frequently that she moved on and wants nothing to do with me. I moved on as well but after I found another girlfriend, she returned to beg my forgiveness and asked me to take her back, which I did. Now I am in a dilemma of having to choose between the two of them. I love them so much but don’t want to take advantage of either of them. Please advise me.