Breaking My Part of the Lease

My question involves a roommate in the State of: PA

I have all intentions of moving out of my apartment that I share with a roommate. Situation is, we unfortunatly were forced to sign a 2 year lease in Jan. or lose our apartment. My roommate has created an environment that I don't feel comfortable living in because her boyfriend (my boyfriend's roommate) spends every night there. In a perfect world I would like to basically trade leases between myself and her boyfriend. My landlord has told me that this is acceptable but if my roommate doesn't find a replacement for the lease or decide to take it over herself that I would be responsible for the remainder of the lease term.
Questions:
1. Can my roommate take any legal action against me if she decides to take over the lease in its entirety?
2. If my roommate is forced to give up the apartment with me because she cannot afford it on her own can she take any legal action against me?
3. When we moved in she paid the entire security deposit and never came to a verbal or written agreement with me about paying her back. Can she now demand that money or will that fall on her?
4. Is it breaking the terms of the lease for her to have a houseguest over as frequently as she does knowing in full that I am against it? He is over every night from the hours of 8pm until he goes to work at 10am. It's not "living" there persay but it is annoying to say the least.

Thank you for any help!

1. Maybe. Your roommate may be able to convince a court that you should continue to pay your share of the rent up to the point in time she is able to find a suitable replacement roommate.

2. What would her damages be?

3. if she takes over the lease, it's not an issue. If it becomes forfeit due to your actions, she could certainly try to recover the money if she sues you.

4. I can't read the lease from here. What restrictions does it include in relation to house guests?