I wouldn't even call myself seriously die-hard compared with other UK fans I know (none of the 9ers though). There is a very long tradition of NFL love in this country, and in fact across Europe (I'm not British born originally). Personally, I've been following the Niners since SB XXIII and lived in the US (on the other side of the country though) in the early 90s including the last SB season. These things tend to make you stick around.
These days I can travel more easily, and it does help that SF is one of the most beautiful cities in the world so I can also have a nice holiday. I've been doing this for quite a few years now, usually combining an away with a home game on back-to-back weeks. E.g. last year it was @SEA then home to the Aints (both losses ), the year before two home games (W vs the Lambs, then that atrocious loss to ATL), the year before that two more losses @NYG and then home to SEA (the pants-down game). Last year of course we also had the "home" win vs Denver at Wembley which was only a Tube ride away for me . So, I've passed the "sticking through the sucking" stage of my fandom with flying colours, I believe. I'm ready for some winning again