Below is a picture of how it looked like in the past in iOS8, then they moved it to Contacts in iOS9, I haven't played with it in iOS10, but the settings moved through my icloud backup from one device to the other, now with iOS11 it got enabled again.
Now in iOS11, when I go to text a person for example , there are all "Recent" options with a blue i , and I don't want that.
When I want to iMessage Lisa, I get all the suggestions of previous conversations I had with Lisa and other contacts
View attachment 719749
When you click the blue i, you can remove them from RECENT for the future and it wont show up anymore.
View attachment 719751
For example if you like to recreate the problem:
1) You text Lisa and Alex together.
2) You close iMessage and a few hours later you want to text just Alex
3) When you text Alex and type in his name , the iphone will suggest to text George and Alex (with a blue i icon next to it)
4) If you tap the blue i icon, you can remove the persons from recent
iOS8 screenshot: