The problem is that you can look all over the internet and read women talking about loving a 'big cock.' I imagine it's similar to guys and big tits. However, it's not exactly the same and there is a lot of pressure on men to satisfy a woman. Size does indeed matter to a point and since size is something that we can't really change, it can become a major point of self-confidence or lack there of. We, after all, want nothing more than to be THE point of absolute pleasure in our woman's lives. Media (porn, tv, movies) has also convinced people in general that if they aren't pleasing you in bed, your SO may stray and go elsewhere (whether this is true or not). We are also aware that women can be nice and say things just for our benefits and so compliments regarding things like penis size can sometimes not be taken very seriously. You knew that it created an area of tension with him from the start since you pointed out that he tensed up during the initial situation. So, to say yes when he asks you in bed in a moment of serious passion (even if you meant it jokingly) can be a bit tough to handle. It's like being with a woman and her saying, oh you're thinking about so and so's huge tits aren't you? or while having sex, "you're thinking about that waitress aren't you?" Some couples are comfortable and enjoy that kind of talk, but if you aren't it can be pretty damaging and difficult to get past. It's an insecurity that can't just be turned off like a light switch. It's there now. Honestly, the way you are referring to his insecurities as being dumb and considering leaving him, means you're prob already out the door, you just need to solidify it. Insecurities can be very debilitating for people. If you're insecure about your weight and keep asking your SO if they are thinking about that skinnier girl you saw at the mall and they said yes, and then you keep asking about all of the skinnier girls they've been with, it affects you. Except you could lose weight. He's stuck with the insecurity, plus knowing that he can't change what he thinks the issue is making him feel even more insecure. On top of that you're attitude about it makes it even worse. I don't blame you, I'd get sick of hearing about it, but you have to come to grips with either leaving him and being done over him being seriously upset about something, or you need to embrace him and reassure him. I think it's stupid for a man to be looked at as weak, dumb, 'insecure little boy' when he's insecure about something. If I were to call a woman an "insecure little girl" because she was upset about her weight, I'd get shit all over for being an insensitive asshole. If his feelings are that dumb, then dump him and move on. People's emotions, feelings, and insecurities come with a relationship it doesn't matter if you are male or female. If you can't deal with that then you shouldn't be in a relationship.