Being Good vs Being Happy An interesting question you have put forth. Personally, I lean towards the idea that being good and being happy, while intertwined, don't necessarily mean the same thing, and that they are't always able to be used when speaking about the same thing.
Let's take the example of the pen for instance. I think that we can agree on a pen being able to take the characteristics of being " a good pen". We can also agree on a pen being the able to fulfill something, such as "the pen is good for writing on the paper". It is both a good pen, being of favorable characteristics, and it is "good for" something which in this case is writing, so it fulfills a purpose.
Now, if we take this same pen which we have agreed is good and is good for something, and we pose the question to the user of the pen and ask him "Are you happy to receive this good pen? Does it satisfy you?" then things can take a dramatically different context.
First off, lets define happiness. You have stated that it is a fulfillment of something and I agree. Happiness is a fulfillment of joy. You are happy because something favorable has happened to you and that has led to joy, which is another way of saying that you are happy. As a matter of fact, the something favorable in question doesn't even need to happen to you, it just has to be what you consider favorable and it has to be something from which you hope to have joy from.
As I have already stated, this is what I see as the difference as I have tried to highlight in my somewhat rambling way. While happiness and good are both fulfillments' of something, happiness is more towards the fulfillment of a desire or feeling. Happiness is much more emotionally entwined. On the other side of things, being good is a fulfillment of a purpose, it is a fulfillment of an object(in this particular scenario with the pen) achieving what it was made to do. And from this we can surmise that being good is somewhat of a more logical train of thought.
When expressing something or someone as being happy we can assume that this is their emotional state. They have fulfilled their innermost desire(which can be, but is not limited to, fulfilling their purpose) and that has brought them to a favorable outcome in which they find joy. When expressing something or someone as being good, we can assume that they have favorable characteristics and that they have achieved their purpose successfully and in decent manner. While something or someone can both be happy and be good, the two are not mutually exclusive and not always able to be used together. And so I surmise that they are distinct and do differ in the various contexts and meanings that they are used in.