The general rule without an agreement otherwise is that you are liable for the entire lease term, whether you leave for a good reason or not. In a situation like this, a landlord is required to try to release it if it is practical, and a court may find that you are only liable for the amount of time it should have taken him to re-rent. Some common wisdom in Washington is that courts feel that 1-2 months is a reasonable time to re-rent, and award damages of 1-2 months if the landlord takes the former tenants to court. This is not a guarantee, however. You signed a contract to stay a year.
If the lease states that there is a 1.5-month fee for early termination, then the lease would govern the situation. Without looking at your actual lease, i can't see anything wrong with that term. If the lease does not say when you have to pay the termination fee, then that is something you will need to agree to with your landlord.
Be sure that you get everything in writing, and signed. Get a signed receipt when you pay the fee, stating what it is for, when it was paid, and that it satisfies all debts between you if that is true. Make sure your notice to terminate is in writing, and, if the lease has a specific time given, that your notice is withing that timeframe. If no time is given, I recommend giving notice at least 20 days before the start of your next rent check is due (before the FIRST day it is due, not at the end of any 'grace' period). 30 days would be better.
My comments are general statements of the law in Washington and are not meant to be legal advice. Specific legal advice requires an in-depth interview, review of past or ongoing court or agency actions or cases, and an evaluation of the special circumstances of each case.
There is no such thing as a lease break fee in Washington unless is is provided for in your contract. As a term lease tenant, you are liable for the lesser of (a) the entire rent for the remainder of your lease or (b) the rent until the landlord finds a new tenant plus rerenting costs. RCW 59.18.310. Your landlord has a duty to make reasonable efforts to rerent the property and, if he does not, he cannot recover any unpaid rent at all.
Your landlord may be proposing a settlement where both you and he agree that you will pay 1.5 months' rent, no more, no less, to be released from the lease. If this is the case and you want to take him up on it, be sure to get that agreement in writing signed by both parties.