<human>: Provide a brief overview of the text.

I went on a few dates with a nice girl maybe 4-5 years ago now. It wasn't the best fit so we stopped see each other. We have both had other girlfriends and boyfriends over this time, both of us now in long-term relationships living with our partners. 

Over these 4-5 years I've maybe seen her 1-2 times completely by chance and for less than 10 minutes, but she texts me sometimes every other day to once every couple weeks without fail. I never initiate these 'conversations' which usually last only a couple simple responses that don't lead anywhere. 

Does anyone else do this or have someone like this in their life? I haven't blocked her or anything because I guess she's nice and I have no real reason to because it's 5 seconds of my time every now and then. I'm just curious WHY?? I think if I ask she would just say "Just saw your name/saw you online and I'm bored." Fair enough, but if that's the reason is that weird to anyone else given our situation? 

My girlfriend and her boyfriend I think both know we message very randomly and don't care. It does not cause a strain or question my own relationship and, as far as I know, hers is pretty solid as well. Just not sure if I should do something. I mean, if this continues for 10 years and we don't see each other, why does she initiate?
<bot>: Went on 3 dates with girl. Several years pass basically without seeing her but she still messages me short, banal conversations regularly. Why? Should I even do anything?