My dick is only 4 inches hard. Every girlfriend I ever had cheated on me with a bigger guy. That answers it for me.
I'm sorry about what's happened to you in the past, but let's clear up a few things here. You said you didn't realise you were below average before watching porn. Well, porn is exactly that. The men you see in those movies are not average, far above it. I think the average is around 5.5-6.5 inches, which is certainly more than enough to provide sexual satisfaction for most women, certainly myself and my girlfriends. You men seem to put so much on size, when you're in a relationship there's a lot more too it. Most women would rather be with someone they have chemistry with and are in sync with than someone who thinks their great in bed just because they're hung like a horse!
As I've said in one of my previous posts, the big cock being better is more of a mental thing than the physical stimulation, so rather than feeling sorry for yourself for being a little less endowed, why not make up for it. As they say, it's not the size of the boat, but the motion of the ocean which counts!
And I seriously, seriously doubt your girlfriends and partners cheated because of the size of your dick! I can guarantee you that there was other issues in your relationship that drove them to cheat. As I said before, if everything was hunky dory, you would have been the ideal sex partner for them and they wouldn't have cared about your size at all. Or definitely not to the point where they cheat on you. I certainly, and no other female I've spoken to before would ever consider cheating on someone we love and are committed too just because of the size of their dick.
I don't mean to sound like some kind of relationship expert here, but I'd strongly suggest you stop putting all your issues down to your dick and you should try to see what could be wrong with you as a person first. You shouldn't be settling to 'serve' just because you think you can't please women. If 'serving' is genuinely what you want to do, then go ahead, but don't do it just because you've convinced yourself falsely that you're an inadequate lover!