Actually, statistically speaking, even 7" girths are practically impossible.
Also, average sized men can not only be as good as "huge" guys. Sometimes they can be better.
Sex is not some one-to-one correlation to penis inches. It's an emotional and/or physical connection.
Your dick size in length (we'll ignore girth because you're probably lying) is well into the 50th percentile. You are not being left because you have an inadequate penis, it is likely they keep leaving you because you are an insecure turd who is so self-centered he doesn't even bother to work at better satisfying his partners.