The standard reading of the song – the singer’s in love alright though he doesn’t want to say it, admit it etc. – gets at something that was in the air a lot in the years after INIL came out. Let me explain.
There’s a great, double-edged scene in Annie Hall (1977) where Annie (Diane Keaton) is ticked off that Alvy (Woody Allen) never says he loves her. Alvy wittily defends his approach to the L-world by saying that it’s too puny etc. for him, and opining that, in general, any word in a real, public language would falsify and diminish his feelings for her etc.. Alvy then launches into saying that he lurrrffs Annie, loaves her, etc.. That’s all quite winning, but it also does register as an evasion. We (and esp. female viewers!) effectively know at that point that Annie and Alvy won’t make it/will eventually split up.
‘New sensitive males’, Alan Alda-ish, Alvy Singer-ish guys, and their downsides became a big, ongoing topic of cultural discussion from the late ’70s on. Part of INIL's power at the time, I suggest, was that it was a leading or at least v. early indicator of that cultural formation: ‘whiny INIL guys and the women who love them too much’ perhaps. And since those questions about men and child-men after feminism haven't gone away since, INIL still 'works' as a piece of stinging observation.
After influencing things like the intro. and feel of The Bee Gees's How Deep is Your Love and the whole production of Billy Joel's Just the Way You Are in the late '70s, in the 1980's INIL musically begat at least:
And half of 10cc itself revisited INIL territory in:
In the '90s, the sound of INIL (and of Paul Mauriat's orchestra) was all over Air's first couple of albums. And INIL itself was on the soundtrack to Sofia Coppola's (in my minority and at-the-time-socially-suicidal view, preposterous) The Virgin Suicides, for whose score Air were otherwise largely responsible. Consider the final party scene from that film:
That's not INIL in that scene (it's Air), but it might as well be.
A Japanese documentary on INIL is up on youtube, and even though only about half of it is in English, it's pretty interesting and worth watching, e.g.:
 How much of Keaton was there in Annie? Ahem, Diane Keaton's family name is 'Hall' (she assumed her mother's 'maiden' name, 'Keaton', for Actors' Equity purposes after college), and her standard, affectionate/'friends call her' name is/was 'Annie'. To say this is not to deny, of course, that Keaton is one of the greatest Hollywood actresses. In the same year as AH, Keaton had the lead in the truly frightening drama, Looking for Mr Goodbar, the Irreversible or Requiem for a Dream of its time. This was an astonishing double for Keaton: giving arguably the best comic, female, lead performance since Stanwyck/Dunne/Hepburn in the same year as the (no-ifs-ands-or-buts) most out-there, hard-R-rated gritty, dramatic performance ever (and Hollywood studios have never gone that dark again). Having dazzled previously in small roles in the Godfather films in particular, Keaton now had two leads that added up to one of the greatest acting years of any film actor ever. It was popularly believed at the time that Keaton's Oscar for AH was in part an award for both her big 1977 roles. That's probably right: the combination left almost nothing to chance. Still, in my view, Keaton probably would (and certainly should) have won the Oscar even if she had had only one film out that year. She was just that good in both cases, and each case was a truly fascinating, industry-peak film.