TENANT breaching lease

[Sean Connolly]

I just recently signed a new tenant in a unit for a 6month lease. It has been two months and he called today and told me they are buying a house and will be out by the end of february. I'm am unsure if my wording in my lease agreement favors his 30day notice or if he is still legally responsible to pay me for full 6 months. It reads as followed.

"This is a (6 month) RENTAL AGREEMENT only! After 6 month's rental payment has been received, this agreement may be terminated by mutual consent of the parties; or by either party giving written notice at least 30 days prior to the end of any monthly period. Any provision of this agreement may be reasonably changed by the LANDLORD in like manner, thus THIS RENTAL ESTABLISHES A 6 month TENANCY ONLY. All parties agree that termination of this agreement without prior notice before 6 months will constitute breach of the tenancy as agreed on page 1, and all Security Deposits shall be forfeited in favor of the LANDLORD as full liquidated damages at Landlord’s option following termination without notice."

Looking for any help and opinions from anyone with any insight or past experience. Especially with experience with Massachusetts Tenant Laws. Thank you in advance.