This was a sad tale to read. I understand exactly where you are coming from and why you had to back out. Sometimes, however, the anticipatory fear is worse than the reality. Many a time I have HAD to do something with absolutely no choice and the fear has gnawed away beforehand. Then when I am actually going through it, I find I get through and add a positive note to my mental experience list. There are loads of tips and avoidances we can use, but the best way to start with a partner is to tell them the straight truth beforehand -they usually don't understand and even find it mildly amusing (OK, so it makes our lives a misery) but remember, this is only an issue in our minds - not theirs, so it's usually not a big deal tho them especially if they love you.
Why are we all putting up with this? Surely hypnotherapy or CBT could help some or most of us?