Leave your husband over him masturbating? If the rest of the world felt this way, the divorce rate would be 100%. If you and he have come to an understanding that this happens - and he is uncomfortable with this admission, and you are equally uncomfortable with thinking about this - well, a mutual don't ask, don't tell policy might be in order.

Privacy issues, even in a trusting marriage are crutial to success..I am the last one to give advice, but if there are deep trust issues, or legit concerns on fidelity, then you should both consider some professional advise.

If there are not real trust issues, then try something new and go and start masturbating with him (online and offline), it might be the next level of excitement for you both...full disclosure, nothing more trusting than masturbating in front of each other.