But won't this feeling of inadequacy keep popping up?

We had a hard time together because she feels inhibited. It is her inhibition that set me off in a thougth spiral of her having tried everything I would ever be able to imagne and me not being interesting enough. Since, she has hinted on previous relationships not being that good (she was married to a narcissitic husband for 19 years and hinted on a previous partner cheating on her for over a year and another person who behaved the same way as her husband).
But still ... I was really old when I had my first experience and in the beginning she spoke of certain things that were fun for her but traumatizing when I was married (to a woman who was constantly bragging about extreme stuff she had done in one night stands and wanted to repeat some of those with me, to which I did not have to courage not say no as I felt a need to prove myself).
To me it feels that my current gf will always have a been-there-done-that feeling when she is with me although her response to even the littlest things does suggest otherwise.

After all, relationships do crumble over unsatisfying sex. Shouldn't I just accept that I will have to spend the rest of my days alone? Sometimes this appears more appealing than the uncertainty and agony I am now going through.

We met during tango classes and we do have a great connection when dancing and can talk about (almost) anything. It is just very hard for her to see me when I suffer from this anxiety. She also struggles with the thoughts - of her having tried everything - I have when I suffer the most.