The thing is that there are more games like you said, but they don´t have Summertime Saga quality or they either are extremely grindy or in an early stage. What´s more a lot of them are implemented ir rpg maker:
Siren´s Domain - Town of Passion ( one of my favourites games but it´s implement in rpg maker )
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Andrealphus - Love and Sex: Second Base ( i fell asleep while trying to find the first sex scene, maybe he has changed it )
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Lurkin Hedgehog - Lust and power ( i found it a bit grindy )
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You should look for honey select games( there are a lot of games , and have a lot of content because making scenes isn´t as hard as another engines )
Also, i strongly recommend you to give rpg maker a chance. I know that they can be a bit annoying, but you´ll lose a lot of good , ehhhh , "moments"? because of this.