I feel like Tenna mirrors Kris's insecurities in a lot of ways. The kid's got mad separation anxiety and still wants mommy to kid their hand in ch1.
Kris is genuinely afraid of the passage of time and growing up knowing they'll eventually have to live on their own. Sans and Toriel's relationship is so upsetting to Kris, not just because it's sad that Toriel's never getting back with Asgore. It's sad because it feels like Toriel is moving on from Kris too.
This obviously isn't true and Toriel does care about Kris but their fears of being abandoned like Tenna are legitimate.