Ciara, from what I was told, the ovum can either travel 'round the long way' (so to speak) to the remaining tube, or just bypass the tube altogether. I don't think it's known exactly why or how this happens, just that it sometimes does. I believe it's also the reason that tubal ligation doesn't always have a 100% success rate. It's pretty freaky though.

When I had my ectopic I was told that even when it is detected very early and it would be possible to repair the tube it is generally recommended to remove rather than repair because it is more likely having another ectopic on a tube that has already experienced one than it is to not conceive with only one tube. I don't think that they really know exactly why an ectopic occurs so maybe there's a bit of bet-hedging with this theory.

Maybe if you are not seeing someone already, you might get some better answers and some fresh hope from a different doctor or FS? If it was a hospital doctor who you spoke to last time, there may be a FS who has more experience in TTC after ectopic. IME, hospitals are more used to treating people from a surgical perspective when they've had a miscarriage or ectopic and not so experienced in helping them conceive afterwards.