Letting go of the past

When I looked back on all the memories that I have made with many people, some closer then others, I could not help but wonder why I can not recreate those memories sometimes? Why does it feel like the world can crumble down upon you at any second if you are not attentive to it at all times? The only reason I have been thinking about those questions is because thats exactly how I felt, not too long ago. Having mixed emotions about a subject, leaving me with a really hard choice to make, I just finally realized that I have to make a choice that would make me happy, not suffer at the cost of someone else's happiness. I understand making a sacrifice yourself to make someone you care about happy, but limits have to be established and not crossed. If you yourself fall into a depression and can not get that person you care about out of theirs, it just is not worth it after some time. In my case the time period was around 2 weeks. I tried and I can acknowledge myself for doing the best that I possibly could but in the end everything pretty much backfired. Now I can leave everything in the past, at least for now and hope that time will solve some problems.