Why not try to find a single guy with whom you can share the same things you have with this one?  Many unmarried couples break up, but at least with a single boyfriend you would be owning an option for the chance of more, if you decide to pursue it.  Then, though you rarely get it, there would be no more "dull ache in [your] chest, because [you are] not able to live with, marry or bear children with [your] boyfriend".

Time goes by faster than you think and you may regret wasting your youth on this guy.  It's tough to rip the band aid off but I think it will be fun once you do - think of all the Tom Hardy look-alikes you could be having fun with ;)