Before you worry about an emotional source to his not having an erection you have to consider his age and a number of other possible problems. It can be a list of issues other than you. He may be telling the truth. Not being able to get an erection can even be for a very short period of time. Consider any physical issues before believing that he does not find you stimulating.
You may be generalizing the fact that you are worried about him finding you attractive because of the online behavior. That may never have been resolved and you are finding it difficult to believe that this is anything but a major problem in your relationship. In fact they are probably not related. If they are than that can be resolved as well. I know he has refused a counselor (marriage counselor) but anything sexual can be resolved in that setting including any feelings regarding physical interactions and how he sees you can be resolved. You may be projecting your insecurities since online behavior onto him. He may still find you attractive and may be a different reason that you have not considered. Reconsider speaking to a counselor
If this has been helpful press accept
This is very embarrassing for a guy and they can overcompensate with this reaction. This is quite common. It is also common for the female to feel in the dark. You used the right word - reassuring. You are going to need some patience but let him know that sexual difficulties do impact the relationship but being honest impacts it less. Let him know that he has your total support and that you would like for him to interact with you about this so you don't feel shut out. Portray understanding and let him know that you don't think less of him.
Give him actual examples of how he is a good partner such as being understanding or being kind and downplay the sexual issues. When you appear as accepting this will decrease the chances that he will shut you out. This is very gradual work however so allow some time. When you point out his positives it makes you approachable. You can let him know that you want to work through this together. It gives him an opening when things do get stressful. Ask him to share why he thinks he is having difficulty and tell him that he can come to you.
Find time for intimacy that doesn't include sex. This will give you a chance to be a couple aside from sex.