So, if I pull away the lighter, that implies my life somehow matters? I naturally don't like pain, that's all, so I'm not going to take the time to hurt myself. And I could train myself, mentally speaking, to enjoy that flame if I really wanted too. I could train myself to not have any reaction at all. But I don't feel like it? This is also irrelevant to living a good or bad lifestyle (which is based upon cultural experience/views, anyway), but all in all it doesn't matter what you do or how you live. Because you yourself have just stated "The sun will eventually die, and so will the universe itself."
1. There are many people that exist, including you and me.
2. We are not immortal, therefore we will die.
If this is correct, then death ultimately erases the fact that you were ever born to begin with -- because you simply 'are not anything' once you die, and in that since you've never existed; there will be no 'you' to make that claim that you did exist. As experience is relative -- your universe has ended (the only universe that you know).
Also, say your kids have memories of you, after you die. You're not a 'manifestation' of those memories, you're not a witnessing presence anywhere at all, therefore they won't/don't matter and are not meaningful. Because your kids will also die, and somebody will hold the memory of them just like they did for you, but now your memorable existence is two steps back, and this goes on and on. The cycle of grief, emotions. Part of the experience now, which has never existed once it ends.