Do that now, because that is what is getting you thru now. But after you "improve" you will most likely meet some one better.
It's not healthy. I'd suggest forgetting about her; you aren't with her for a reason.
it is not bad to think of your ex.. you have the right to think about whatever you want..
I think of all of my ex's all the time when I'm single. I think its a moderate betrayal to think of an ex frequently while in an intimate relationship
If you wonder where your heart is, look at where your mind goes when it wonders.