Just another thought on top of the others here....the vasectomy might have had the unintended consiquence of making him feel much more relaxed about sex. What I mean is, if it was done as a birth control measure, it might have had the benefit of him knowing he won't be starting any more kids with you, and that sex as often as he likes it, will be much more satisfying then previous, when he may have (unconsciously?) felt he was playing russian roulette. Women have the pill (which can be forgotten and fail) or other methods all of which can fail (excepting tubal ligation of course--which can, but rarely does fail) and men have condomns which can fail....but common thinking holds that a vasectomy is perminant and therefore 'freeing'.

Masturbating in front of you unexpectedly is odd, if he hasn't done so before, but he might be trying to see what turns you on (as it does turn on some women to watch)...of course, just ASKING would be better, but have you always had an open conversational sex life? If not, he may find it difficult to talk to you about experimentation.

Also, by asking him if something is wrong and then asking if he still loves/wants to be married to you (after he says nothing is wrong) sends a message to him that in your opinion, something IS wrong. He became silent, no doubt as a defensive mechansm. I'm not saying that's the right thing to do, but I certainly understand his motivation.

Marriage counselling might be a way to help him open up about what he's feeling, and what he wants, and a way for you to get answers without feeling you've done something wrong (and especially putting out there for him that you're feeling unhappy with him--because, trust me...that's what he took from your questions, even tho I'm pretty sure you didn't mean it that way). It's natural for you to feel concerned that you've done something wrong--but men (and women) when asked that type of question, automatically think THEY'VE done something wrong and rather than further the conversation, it more than likely shuts it down as both the questioner (accuser) and the one being questioned (accused) will automatically go to their respective corners to either pout, or lick self-inflicted wounds.

A counsellor can provide the objectivity you might need, to get past the awkwardness of the inquiry and hopefully make communication about this situation easier and more productive.

Good luck!