Ummm - lots of things. Early 1980s is my student days and I was having a lot of fun living in London until the mid 1980s, so New Romantics etc transport me straight back, misty-eyed, to being about 20 and in love for the first time. I got the 12" of Joy Division's Love Will Tear Us Apart for my 19th birthday and any time I hear that I'm instantly back in that student flat.
I recently compiled a long playlist that goes with a long, complex and occasionally infuriating relationship that still has a lot of unwritten history about it and I play that on long journeys. That's pretty eclectic - it includes Dido, the Goo Goo Dolls, Snow Patrol, Sia, some dance music - and it still gets added to as the relationship has a lot of yet-to-be-written history about it.
But my whole life has been marked by music - my American and Canadian childhood in the 1960s and 1970s, school in England, student days, living in London ... *misty eyed* *feels old
I can empathise with your remembering a relationship through the music that accompanied it. The music of the late 1990's, for example, can cause me exquisite pain when I hear it. And yet, I am forever assembling long playlists of it!
At this very moment I'm listening to John Cooper Clarke (punk poet, bard of salford etc)
As for soundtrack of my life, uuummmm... I would says Smiths, Joy Division / New Order, Durutti Column (ie most of Manchester's output from late 70's to early 90's), but my record collection covers many other bases like Killers, Tangerine Dream, Frank Zappa, a lot of late 60's Stax & Atlantic stuff, it all depends on my mood.
As an example of my varied taste, I was DJing at an alternative night and decided to drop some Betty Boo in the middle of a set mainly containing stuff like nine inch nails. I was almost killed, but was unrepentant, people can be too precious about their music.