My question involves landlord-tenant law in the State of: Massachusetts

Here's the story, I'm supposed to sublease an apartment come January in Boston. Back in June, I signed a sublease agreement with the person currently living in the apartment. He was supposed to go home for an internship in January and I was going to move in. Come September, he changed his mind and decided he wanted to stick around next semester and he asked me if I was willing to work something out. I said, sure I'm flexible, you want to change the sublease so you have to do the grunt work (find another apartment), as long as you find a place within the same distance from campus, same price, and with people I know (same conditions as the place I was going to sublet) we can work something out. It's been two months, he hasn't been able to find anything and from what I've gathered at this point has given up on the apartment hunt and is trying to weasel his way out of the sublease agreement.

Here is the sublet clause from the original lease:

The Lessee shall not assign nor underlet any part of the whole of the leased premises, nor shall permit the leased premises to be occupied for a period longer than a temporary visit by anyone except the individuals specifically named in the first paragraph of this lease, their spouses, and any children born to them during the term of this lease or any extension or renewal thereof without first obtaining on each occasion the assent in writing of the Lessor.

My questions are thus:

1) Since a sublease agreement was signed between me and the original lessee but not between me, the lessee, and the lessor, is our sublease agreement valid? Note, the sublease wouldn't take place until January and I would go to the lessor to get an agreement with them before moving in.

2) If the sublease agreement is valid, what damages would the other party be responsible for as a result of breaking the agreement (costs to find a new apartment, travel costs, rent difference, etc.)?

3) The other party doesn't have a copy of the sublease agreement, am I legally obligated to give it to them?

thanks for your help.