Idk whether my answer is 100 percent accurate or not, but from what I know, aishiteiru means I love you in Japanese, is more formal, for suki desu, means I like you, which is not so formal compare to aishiteru, this is all I know, I hope I answered your question
Aishiteru/koishiteru is more intimate so I was hoping they both said that, instead of Suki because Suki is first level confession thing. It's just like saying 'I really like you'
It might be suki desu cause in japan people normally Don’t say aishiteru. It seems weird for them to say that so they Suki desu which can translate to I like you but in some cases it can also mean I love you, but then again its a manga so it could be aishiteru.
I really want to know if that 'I love you' was "Aishiteiru' or just 'Suki desu'