A little too long.. When your remembering her after time has passed the brain sometimes edits out the bad parts but not the good. There's a reason you went your separate ways, so get yourself busy and start looking for a new start.
Well you have to move on at some point. There is nothing to be gained from keeping her still in your mind. There is a whole world out there with other women, and one of them is probably waiting to meet you. Take your mind off your ex by taking up a hobby/hobbies in the meantime.
If you use it to ********** its ok.