It's not the problem here. It's more like "why she's lying about things she did with her ex, while insisting that she's honest?".
It can be a problem and it's severity is dependent mainly on how your mind works / it's current formation.
For some it'd be relationship ending as their imagination is too powerful, and perhaps combined with intrusive thoughts could make it quite painful for them.
Others it may just be a sub-conscious understanding of the fact it's objectively less romantically pure and their intimacy is just slightly stunted.
And some may not mind at all due to their temperament.
But anyway I'm just being pedantic and I believe Exqisitus was joking.