You could always come out and be honest. "I was thinking about sex. I don't think that we should do it just yet, but I want to know what you think. So what's your opinion?"

my line anytime i bring something like that up (because i'm awkward in general in terms of verbalizing thoughts, and even worse when it comes to an awkward subject), "i don't want this to sound weird, but i had just been thinking, and i was wondering what your thoughts about sex were?" a brief preface would be fine, but sugar coating it isn't necessary. just come out and ask, it's usually the best policy.

you could like ask him for his opinion on something like, 'how long do you think a person should wait before having sex with their partner' or give your opinion first like 'i always like to make sure a guy is committed enough before i think of sex with him. what do u think?' or 'i think this whole no sex before marriage is bull****. what do u think?' something like that. bring it out casually like as part of a getting-to-know-each-other conversation, or a general discussion. from what he answers, you can get an idea of his views on it. plus he also gets to know your opinion about sex. it goes a good way in avoiding any embarassment and tells you when would be a good time to suggest sex (or if he gives the impression he's not interested in sex, it saves the trouble of asking) . and when you do, part of it is already mutual understanding and expected by the partner, so it goes pretty smooth.

after 3 & 1/2 years you guys must really know one anoyher well can't you just be frank with him ? if he has never mentioned it he probably does not want you to feel pushed. is he a virgin ? he may feel awkward and not wanting to put you on the spot. unfortunately some of us grow up thinking that girls don't care much for sex