Being on friendly terms with past partners is another one. Or for that matter cherishing the memories of the good times with those partners. A lot of people seem to think that after a breakup you should hate your ex forever and burn all pictures, throw away any object they ever gave you,... but that is actually quite unhealthy (unless abuse or stalking or similar things were involved of course). If a relationship does not work out that doesn't mean that other options, such as friendship, might not be on the table and even if they aren't that doesn't mean you can't treat each other like regular acquaintances when you randomly meet somewhere. Obviously they might not be an option immediately after a breakup but once time has dulled the pain a bit a friendship is absolutely possible with someone you initially shared enough interests with to try a relationship.