Because your lease ran out and you have not signed a new lease, your tenancy is now a month-to-month tenancy. This means that you can terminate without giving any reason, as long as you give 30 days' notice in writing to the landlord.
You also have the right to feel safe in your home. You can advise the landlord of the unauthorized tenant (the boyfriend) and of your concerns about him. However, this could increase the tension in your home until the problem is resolved.
Have you spoken with your roommate about your feelings? You can suggest that she and her boyfriend sign a new lease and allow you to move out. You could also suggest that a new roommate take over your spot in the rental. Additionally, you could tell her that her boyfriend needs to pay his share of rent if he's going to live there.
Once you terminate your lease and move out, the landlord has 31 days to return your security deposit or to give a written statement to you justifying the basis of any withholding. Be sure that when you do move, you forward your mail with the landlord and with the post office, so that he can find you to refund your money.
You have several options, but simply moving out without giving notice is not one of them.