Everything in life is going to break down into nothing. The universe itself is gonna break down into nothingness. This nothingness is called entropy--from order into chaos. Good will always break down into pain and there is always some price to pay for whatever good you recieve. For example: if I pick up some change on the street then I benefit from that but there is a price to pay for picking up that change. I may not pay the price for taking that change, but someone else will. Like, a homeless man may have seen it and it would benefit him by being able to buy something from a vending machine but since it's not there he's the one paying the price for me picking up the change.

This can extend for every gain in life, for everything good that may ever happen, there is a price to pay for that good. If you receive good then you will either pay the price for that good or someone else will. For every action there is an equal and opposite reaction. But conversely, if something bad happens to you then it's just bad because that's the natural state of things.  However, it's possible to make a "down payment" of sorts on pain. If you're willing to make a down payment on pain then it's possible to recieve good in exchange for that. Yet, it's not guaranteed you will recieve good. Why? Because your pain might lead to someone else's good or the universe just decides what you're doing isn't good.

Ultimately pain is the natural state of things and everyone is destined to be miserable. I'm really curious to know what everyone's thoughts on this theory is.

1. Entropy is the total number of ways in which a system can be arranged. Intuitively, this is recognized as disorder, not nothingness. Now energy becomes unusable as entropy increases (which it always does in a closed system) and that is what is meant by your phrasing of "nothingness."

2. Entropy only must increase in an closed system (the universe.) This does not mean that locally entropy always increases. In fact, the existence of life, and other forms of order refutes such a premise. You are right, there is a cost, and that cost is energy, and that energy must come from somewhere. The energy is only changed though, not destroyed. In a closed system greater entropy => more unusable energy (as a percentage.) In an open system this is not the case though.

*This is where science ends, and philosophy/ethics/social science begins.*

3. "Good"and "bad" are subjective values partly based on human nature, but also based on individual variety. There is no physical natural preset of what is good and what is bad, only a human one. The connection with entropy (a physical model) you are trying to make is quite confusing to me. You involve a discussion of scarcity, which seems more relevant to economics and praxeology more than physics. Physics says nothing of "good" and "bad."