I have been with my BF 5 years next spring. We live 45 miles apart in our own houses and we are both very happy with this. We see each other (most) weekends & for holidays. It's great - the best of both worlds.
We are both in our late 40's - I have been married twice & until my daughter left home 18 months ago I had never lived fully alone. I love it. He has never married or had children, but has lived all over the world, travelled, been independent. Has only lived briefly with 2 women.
We both like our independence & our own space. I like time to myself, as does he. I have loads of friends (he doesn't!!) & am never lonely, but I do like being alone.
Some of our friends & family think it's strange - I know my mum would love me to shack up with him, but dad understands why we're hesitant. why should we because it's 'expected'? Maybe, just maybe one day we might - if we move away together & live near the sea (a dream of both of ours), but for now our arrangement works.