Is the ending of the play optimistic or pessimistic?

That depends upon how you look at it. I believe that Tom carried a very sad picture of his sister and a lot of regrets around for the rest of his life. I also believe he went on to do what he wanted.... that for whatever regrets he carried..... he still led a very happy life. As for Laura, I'd like to think she went to school, and then onto work. Tom's leaving meant the women would have to provide for themselves, and in the meantime, maybe Laura branched out and made new friends. If I'm right, Amanda would have acquired a sense of freedom too..... but I guess we will never know.