I'm anti - porn because of the way that it causes intimacy problems in relationships. It's a dangerous practice to be involved in, because of the insidious way it makes people addicted to it.
He is using a lot of porn and is now finding it hard to stop his usage, one of the signs of addiction right there.
The children seeing this just doesn't even bear thinking about.
You say you probably have sex with him about once a week, if he instigates it, but that's not because you don't want to/or don't enjoy it.
That statement right there is your problem, sex once per week isn't enough for him, I'm simply stating fact. It's not meant to denigrate you in any way, but If you really were interested in sex, you would instigate it, but you don't. Is there any reason for this, that maybe you haven't stated. I mean we're you always a once a week couple?. What's his take on this.?. Looking up his ex on Facebook is just another symptom of this problem. I mean you say you feel insecure and inadequate, he says he turned to porn because of lack of sex, so he feels insecure and inadequate, because his wife doesn't initiate sex with him.
He is telling you what it's all about. I'm not in any way agreeing with him using porn. You are sexually not on the same page. Compromise is needed, or if you simply aren't sexually interested in him, you need to split up. I not expecting my opinion to be popular, but I'm sure if your husband is honest, it's exactly what he's thinking. And you saying at the end of your post that you don't want him anywhere near you says it all really. Therin lies the problem.