Interesting question. Glad you were fine OP.
To respond to why someone said it was selfish, it is selfish as in while you may have some immunity you can still pass it on to others. So you may not get it again but you can still infect your friend, who infects their mother, who in the worse case scenario dies. The whole, well I'm fine is part of the problem at why the cases are increasing. Not saying that's what you are saying, but just part of the attitude problem attitudes towards this virus overall.
There is also the side of the coin that we have largely abandoned herd immunity theory awhile ago. It seems you WILL have some immunity from the virus but it's short lived. Different people have shown to have substantially different degrees of immunity, some having immunity many many months on and others losing it weeks later. It is shown to decrease over time in all people. So there is now way of saying you are ok for 6 months, 12 months or even 1 month later.
The interesting thing about the case that was published recently was that he has tested negative a few times after having tested positive for it, first exposure was mild but the second case was only a couple of months later I think (off the top of my head), it's one of the few confirmed cases because he had a positive, followed by 2 negatives and then a positive, whereas there could be a lot more cases like this but we don't have the actual evidence to confirm it.
That short of a time between the cases is alarming as we assumed even with diminished resistance, you would have had a lot longer than that.
The second interesting thing was in his case the second time he had it he was more severely affected than the first. He actually needed hospitalised that time although fully recovered. That is alarming as typically when we are exposed to viruses we are better as dealing with them if exposed to them again, so that is atypical of how we would expect the virus to act. I guess alarmingly it may suggest that subsequent exposures could potentiality be worse than initial exposure.
However, that's all based off one case, so we can't really take evidence form it, other than to say, we don't know enough about the virus yet and therefore anyone, previous confirmed cases or not, is at risk.