I think you're looking at things in a materialistic, perhaps yes objective, but strictly mathematical way.

Nobody would ever deny that someone truly in love will only ever have the best intimacy with the person they love. So currently, no matter how many objective features someone else scores better on, the end result of lovemaking is less enjoyable with them than with you.

Avoid my own big issue: theorizing that if both you and the other guy were candidates for ONS, she'd pick the other guy. That is a completely imaginary fantasy you create to destroy your self-value. I wish I had advice regarding this, too, but all I could feel about it was I'd just have to settle with being less sexually attractive and more romantically attractive.