What does a #1 next to my sent texts mean?

[KrystaalPistol]

I have a galaxy note 5 and my boyfriend has a galaxy s7 so we do use enhanced messaging. So whenever i send a message theres like a 1 next to my message and some times it disappears. Before i udated to marshmallow it would say if my message was read. Now im not sure if that was removed? Anyone know what this means?
I include two pictures. One is after time has passed i guess? & the other is when i just sent a text.

 

[Big_Berny]

Maybe that's just a bug?

 

[BrockS.]

Just a guess but maybe that is the number of unread messages on his end.