Maybe I made a mistake

So me and my gf broke up last week but ever since she's been acting good like she doesn't care when we were together I didn't feel love for her at all so Since we broke up I've been crying either because she was like my first girlfriend and I'm afraid of change or because I'm going to be leaving my dogs behind either way I'm hurt so to get my mind off of it I started talking to this girl I used to talk to and now she wants me to be her's but she's not stable ahe smokes drink etc my recently Ex girlfriend is kinda more stable than her she has more going for her I should say I don't know like could I miss my ex But I know she's not good for me at all