Catching your husband like that was obvious a shock to you, but it appears that there is a reason for it. (by the way there is nothing abnormal about him masturbating). Men usually do this a lot when their young, which of course the time guys are the most sexual aroused easily, but as they grow older then tend not to do it so often.

If your truthful with yourself you know why he was doing this when you caught him unexpectedly, for in your own words you say you have unresolved marriage issues plus that you only made love with him once or twice a month. The unresolved marriage issues are causing him stress and he feels alone, and then of course he is just a hot blooded man who has to relive the sexual tensions he gets from time to time. Your marriage is indeed in a dangerous place right now, and if the two of you don't talk about it, its going to collapsed. When any of us feel we are not loved anymore, then eventually he will be open to affairs rather than having to masturbate.

I can understand your reason for being shocked, but you have to remember men are made up differently to us, they are able to detach love & sex as two different things. Whereas we tend to associate love with sex. Also its hurt your pride, and leaves you thinking that he does not fancy you anymore, and this is not true, men are different. But if you don't resolve your marriage issues, sooner or later if the right circumstance comes along, he will probably cheat.

You both have a right to be happy in life and in marriage, its not fair to either of you to just go along because marriage is convenient or your scared to be on yourself again, and its not to late to try and put things right, but you both need to hear and listen to what each has to say, even though it might hurt you. Have you thought about going to a Marriage Guidance Councillor ?

Try to bring that spark back into your marriage, but if its not possible then let each other go free.

Good Luck