OK, let's try looking at this from your perspective, rather than theirs.
I understand that you are surprised and upset by this revelation, and you feel doubly hurt - one because your husband is looking at pictures of women, and two because he attempted to evade the issue.
So, you need to take a step back and think calmly about what has happened, why, and the way forward for both of you.
As has been suggested, this will not be the first time your husband has looked at pictures like this - the advance of the Internet makes access to images limitless, and most men are tempted but ...
this does not in any way refllect ohhis attitude towards, or feelings for you and your marriage.
Looking at erotica is a sseriously strong inbuilt impulse in men - there is a multi-billion pound world-wide industry built on it - and it relies on the simple fact that, given an opportunity, most men will look at picturers of attractive young women, so rest assured, your husband is not in any way abnormal in doing this.
It is important to grasp the fundamental fact of the male psyche - looking at a stranger does not affect his thoughts, attitude, or love for you - it's a transient pleasure, like eating a cream cake - there one minute, gone the next, it's literallly that important in the scehem of things.
You feel shocked and betrayed because this is a side of your husband's nature which you knew nothing about, and it has made you doubt him as a husband and partner. Please don't let it . His rather clumsy attempt to difuse the situation was caused as much by embarassment as any desire to deceive you - he feels foolish for bieng caught, and guilty because he knows he has hurt you.
You need to have an honest talk about this. Explain that it is his secrecy and the shock that has upset you, but assure him that he is still the same person he has always been (because he is!) and