I'd prefer it if her breasts were smaller. The best ones are the ones who fit right into the palm of your hand. I've never really found very big breasts attractive. While I don't love the complete washboard style that much, I prefer a more modest bust.
Also, the mc isn't praiseworthy at all for not taking the next step and holding it in. He should've done so far ago. He's just being a selfish coward right now. She wants it, so how about you god damn satisfy her? Do your job as a man and make her feel safe. There isn't any chance of pregnancy if you take the proper measures against it. If you're so damn worried about that, you could just go for the backdoor and use hands or toys on the front. What's the big deal.
Seriously, this kind of shit is never kindness or admirable. It's just stupid and foolish.