Which girl should I go with?

I have two girls and I'm stuck between which one I want to try to be with. One is my current girlfriend of only 4 days so far, the other is my ex who misses me a whole lot ._. it's a tough choice. One is kinda hard to trust while I won't get to talk with the other one much since I'm going 4 hours away to college (my ex is also going to the same college too). Me and my ex are both currently in relationships though, but I believe she would break things off with him to be with me, I don't want to put all my money on it though since all I know is that she really misses me and she is being very nice and close to me lately and has even been saying how she shouldn't have broken up with me.

It's a really tough choice, since one I know I'll be around but I don't want to hurt the other one. I care very much for both of them, and I don't want to hurt anyone, but I want to be with someone I can be happy with. I don't know what to do...