The answer to why I feel moments of terror - not intended as a reversal - is tied to the fact that I have great relationships today in which I can hear and be heard, but I view the connections as temporary, affected by time and health and where I live and work.
Yes, the relationships probably are temporary. Many don't live in a close knit family community anymore, many of us move around a lot. Some of the best friends I had back in the day were when I was in the military, I don't have contact with them anymore. Lots of good friends were at jobs, I don't work there anymore. If one moves from one community to another it certainly means changing church fellowship as well.
It sort of brings to mind a passage from the Sermon on the Mount --
"But seek ye first the kingdom of God, and his righteousness; and all these things shall be added unto you. Take therefore no thought for the morrow: for the morrow shall take thought for the things of itself. Sufficient unto the day is the evil thereof."
The context of the Sermon and it's passages get debated quite a bit though here I think there is a valid precept or teaching.
As for retirement I can tell you what one family acquaintance did. The guy was a teacher and had a pretty good retirement. Leaving work and retiring meant leaving his secular community of fellowship. Even though he had a house he sold it at that point, he moved into a retirement community on an old campus that was remodeled into retirement condos. That was his new community, he didn't just live alone in his house.
Who knows what option you will have when that time comes but there will always be some type of opportunity.
As for posting in a forum different things come to mind for different people who may choose to respond. One thing that came to mind for me was that some have taken [I'd even say twisted] the passage in 1 Corinthians 7:7 "For I would that all men were even as I myself. But every man hath his proper gift of God, one after this manner, and another after that." Into a whole new thing that Paul isn't exactly teaching, "The Gift of Being Single".
Here in the modern church there is sort of a "monkey see monkey do" thing going on [evolutionary pun not intended].
One says amen, they all say amen, one starts having testimony night they all start having testimony night, one preaches a sermon on the gift of being single they all start preaching a sermon on the gift of being single.
I have had friends point these things out to me, they were pretty much filled with charges of being selfish or stating that single Christians should be super-Christians or at least super members of society bringing up famous bachelors like Newton, Pascal and DaVinci. One guy even highly touted the fact that singles will have lots of extra money to give to the church, no doubt he had his own church org in mind.
Any Christian looking into the issue or doing web searches is likely to run into these things so I commented on it.
As for fellowship I still think that the small group model certain churches use does indeed develop close fellowship but it probably won't last past the next time you move. Anyone in a church is supposed to be in fellowship with brothers and sisters. If that's not the case it's possible to visit other churches that do have this type of fellowship in a less formal way. I can sort of understand the problem of stuffy and formal churches, most of my family spent time in churches like that. If somebody had a problem the people at church were the last they wanted to talk to, it was like saying you were the only one in church with problems. If so and so is talking to pastor a lot it was probably a bad thing not a good thing. It's necessary to escape that type of thinking to have true fellowship.