I have two questions. My first questions is: When I was about twelve I was experimenting with masturbation and I accidentally broke my hymen does that mean I am no longer a virgin? And my second question is: Is it a sin if you fantasize about having sex with your future imaginary husband.
A virgin is someone who has no experience in sex. Breaking your own hymen doesn't count as having sex. In ancient days it would have meant that you would have had a harder time proving that you really never had sex before. But in today's time such proof isn't needed and there are a number of ways that a girl's hymen might be broken that has nothing to do with sex. Thus, you are still a virgin.
In the Song of Solomon, the heroine on a few occasions caught herself imagining what sex would be like with her future husband. This isn't quite the same as the situation you describe since she was already engaged and knew who she would be marrying. Yet, the warning is still important. "I charge you, O daughters of Jerusalem, by the gazelles or by the does of the field, do not stir up nor awaken love until it pleases" (Song of Solomon 2:7). Imagine seeing a deer in a field and wanting to pet it. If you rushed up to it, the deer would dash away and you would not get what you desired. But if you moved quietly and gently, letting the deer see that it is safe having you around, then you might actually get to touch the deer. The point is that love is like that. When people try to rush love, they actually drive it away. Love is something that needs to develop on its own and at its own pace.
One problem with fantasies is that it sets up expectations within a person of what sex ought to be like, yet the imagination isn't limited, so therefore unreasonable expectations are created.
Another problem is that it awakens desires where the focus is on the physical aspects of the relationship instead of the people involved. The result is that when temptation comes to have sex with someone you do plan to marry, it becomes a bit easier to given it because you had been thinking about it for a long time.
Sure, there are going to be fantasies, but keep them out of the bed for right now. Don't rush your life.