1. I have learned that very few relationships last “forever.” Forever is a long time and the reasons and seasons of our lives ebb and flow as do our relationships.
2. I have learned that you really do find out who your true friends are when the chips are down. Friends of only a few years can often turn out to be more genuine than friends you have known for 20 or 30 years.
3. I have learned that knowing others personality types and the way they roll can really help you when you are annoyed at how others show up. Everyone should study Meyers Briggs and other personality theory for a better understanding of self and others IMO.
4. I have learned we never, really, know anyone as well as we think we do, including ourselves. There are always surprises to be discovered and change is a constant if one is still alive and kicking.
5. I have learned as @Haleth mentions, that being single is far preferable, infact joyful, opposed to being in a non-working relationship and that liking your own company and being content is very important for true happiness. Too many relationship dependent people out there looking for someone else to fill up their empty places.