I suppose it was inevitable but it is still a drag.
Sitters have said that they can't provide babysitters any more, not because DS3 has special needs but because occasionally needs a pull-up change in the evenings. And their babysitters are not allowed to change a child who is any older than two.
DH and I have no family nearby and although we have tried getting friends to babysit it just never seems to have worked - mainly because they haven't asked us to babysit for their children in return so we feel guilty about asking them again (this has always been the case, ever since DS1 was a baby - nothing to do with DS3's autism).
As I say, it was kind of inevitable that this would happen one day but it is still a bit depressing . DH and I don't go out together that often - maybe once every two months - but it has been kind of a lifeline.