I don't think Spamton was unaware that Tenna genuinely misses him.
I think part of why Spamton is so pissed off at Tenna, BECAUSE Tenna was so clingy and inconsiderate of Spamton's desire for freedom. Tenna asserting his control and trying to get Spamton's secret through a contract is exactly what led Spamton to loosing his benefactor and his [Freedom].
His whole [Broken home] speech in the weird route feels like he knew about Tenna's declining mental health. He'a venting about how Tenna never had his issues sorted out and will end up alone like he deeply feared BECAUSE of it. Because Spamton knows the prophecy too, he's definitely aware that Tenna does get worse leading to all the TV world darkners abandoning him.
Spamton in dealmaker/puppetscarf form likely knew that Tenna was being the fakest IDGAFer throughout ch3. He was probably pissed the whole time that Tenna says all these emotionally charged things while pretending they're logical business decision.
When he pops out during the Pipis scene he isn't 100% sincerely happy, it felt more like he was going "I told you so!" and about to rub it in his face, except that Tenna literally didn't recognize him.
Don't get me wrong, Spamton likely IS happy that Tenna does care afterall, but he's still mad the whole time Tenna constantly tried to push him under the rug and pretend he didn't care, publicly. Imagine this happened to you in real life you, would be pissed too.
I think what Spamton wanted in the past was for Tenna to actually open up to him and trust him. He might've been convinced by the "sweet talk" that Tenna was being sincere for once and showing a side of vulnerability, but that wasn't the case. Their relationship ended bitterly with both of them manipulating eachother and repressing their true feelings.