Hi Kiki,
I must say it's heartening to read that other people like you and Alex have had a similar experience to us. My partner and I are 37 and 35 and have been here nearly five years. We have great jobs, a lovely (albeit extortionate!) rented home in a nice area but we feel that our life is lacking good friendships. We've met so many people since we moved here, and like you say we've really made an effort to make friends but seem to have not met many like minded people and between us have a handful of friends spending the majority of our weekend's just the two of us which can feel lonely.
We discuss endlessly moving back versus staying here. Our quality of life is so much better here fiscally and job wise but I worry that my 30's are passing me by without the warmth of good friendships. Our decision at the moment is to return for a holiday next summer and probably move back two years from then.
Good luck with your decision, it's not easy!
Lucylou