There is nothing wrong with what you have mentioned about pretending to have reached climax, rather it is indicative of the intelligence and wisdom with which Allaah has blessed you and of your good treatment of your husband. We ask Allaah to reward you for that and to make it a cause of happiness for you and your husband.
It is not lying if you tell him that you enjoyed it, meaning that you only enjoyed seeing him.
Masturbation is haraam, including the way that you have mentioned. What you have to do is to stop doing that, and repent from what has happened in the past. You should understand that this is may reduce your pleasure with your husband, and make the problem that you are suffering worse.
This problem is usually due to two main reasons:
1 – The husband’s not understanding the problem or not having any interest in solving it after he finds out about it. From your question it seems that your husband is keen to make you enjoy it, and he understands that a woman may be deprived of that. Hence the way to deal with it is to be frank about it, in a way that will not hurt his feelings or spoil his enjoyment. Perhaps as time goes by you will find an opportunity to tell him, in an appropriate manner, so that you will not be forced to resort to something haraam and you will be able to enjoy that which Allaah has permitted for you.
2 – It may be due to the nature of the husband or wife, in terms of strength or weakness of desire. This can be dealt with by natural means, medication or psychological preparation and doing that which will increase love, and the most important is the wish of each spouse to fulfil the desire of the other.
See also question no. 23390.
And Allaah knows best.