I really love this song by SHIROSE (WHITE JAM) and I have been listening to it for ages, but for the life of me, I can't understand what the title means. 「９つも離れた君との恋」 I understand without the ９つも but it's a difficult clumsy translation: "The love with you who I was separated from". But what is the ９つも actually grammatically doing in this sentence? If you need a little more context from the song, the lyrics are written from texts he sent to his ex, which I thought was a really interesting concept, and great to analyse this use of language. If someone could explain I'd appreciate it so much! Thank you!
～つ can refer to one's age. See: In 星の王子さま, what is this 六つのとき?
So it's "The love with you who is as many as 9 years apart in age". 君 can be either younger or older. (Judging from the whole lyrics, I feel 君 is 9 years younger because she seems to be better at SNS, but you cannot tell this from the title alone.)