Split between the 2

I've been on and off friends with my first love (DD) every since we broke up in 2015. We still loved each other like we were in a relationship tho. September 2016 my best friend (EC) admitted his crush on me. So at that point I was trying to make up my mind. In December I was in a relationship with EC. Me and DD still talked to check up on each other. EC and DD knew about each others roles. DD is in jail and we made some promises about always being there for one another even through the hurt and pain. Me and EC were together for 6 months and we recently broke up over authority issues. I started having these emotion flare ups about DD that I can't control. They make me sit and wonder if we were meant to be and not EC and basically vice versa. I told EC about these feelings and he wants me to kill the feelings but its easier said than done. We both cried about it. I don't want him to love me when he can't be the only one I think about. I feel like im gonna have to learn this the hard way and I dont want to choose the relationship that is trash and then run to the other. My biggest thought on this is that I'm only 17 and I feel like im pressuring myself to settle down. I know which guy treats me better but the feelings from the past cloud my judgement. Please give me some advice or what you did/would do given the situation.