benignuman – I’m using the Shach’s language of “Margilin L’Ervah” in YD 195. So yes, that does depend on intent in many scenarios. The source (Avos D’Rav Nassan) compares it to Chibuk V’Nishuk.
Where I think we disagree is that having fun together is bolstering the “non-platonic”ness of the relationship, just because the relationship will culminate in a non-platonic fashion (hopefully). One can and should bolster the “platonic” aspect of a relationship even when they are married (during certain times .), and that doesn’t mean a couple can’t talk and laugh together as long is it is not “Margilin L’Ervah” (For example, one tells over something funny that their child did that day).