Let's begin.
If you were here in the room with me, I'd ask you questions, but I'm going to shortcut that process and first offer this advice: Check yourself. Meaning, monitor your feelings. Honestly. At some point, what you describe as "sadness" may manifest itself as anger. Against yourself or others. The members of this forum are smarter than me and have advised you to dump the woman who is making you feel inadequate.
What have you learned?
The number one responsibility of this forum is to promote self love and respect for others. Regardless of cock size. Which means, people bragging about their cocks need help in equal measure to brothers worried about inadequacy. It's all an illusion, but it is connected to the most fundamental skill that we all need to do something important with our lives:
The ability to respect ourselves, and to define limits as to what we will own in terms of self improvement and what we will be hard-wired to presume as me without need or regard for enhancement.
A man named Poypeye once said: I'sg am what I am."
Muthafucker seemed pretty happy with himself too.
In your familial, friendship, business, social, and spiritual relationships with people, you will receive feedback and pressure to be something that you are not. Learning to sort through what you can, and should change is a life long art. I hope that you listen to the wisdom you've already received from the forum.
If after hearing all of the people exhorting to you that you are a fine man as-is you still feel a sense of inadequacy, I need you to be open to the possibility that you have something that needs to be worked on in a therapeutic setting. That is not a negative thing, or an insult -- to the contrary, I think that it is so clear that there is nothing wrong with your dick that if you nonetheless feel that way, there may be something more "hurtful" to your ability to experience happiness at play.
Men with broken bodies, in the millions, have loving and happy relationships. Every man on this site --if he's lucky and less foolish than some of the posts suggest -- will live to an age where their cocks will be non-factors in their lives. Yet they thrive. But, here you are, young and virile -- amidst those others, allowing your spirit to be broken by the brain of a dingbat.
At a certain level, feeling inadequate cockitudinally has nothing to do with wanting to satisfy a woman, it is displaced desire to enjoy another guys cock. If you're checking out cock pictures on the net and feeling like you'd want that size cock you're not shopping, you're admiring. Don't take that as an insult. I just got done sucking a cock recently, so I'm no hypocrite. I love pussy, but a nice cock is a beautiful thing. If you can't beat 'em, you're problem may be that you need to join them. I never thought about my own cock while a prick was throbbing in my mouth. Be open to what is in your heart. It's not an authentically heterosexual act to window shop other guy's cocks.