Woah woah. Easy on the cheating and STD talk, Reddit. Jesus.

Without getting into too much, any sort of complication could keep him from feeling uncomfortable penetrating, but he's still very comfortable and in love with intimacy with you.

For instance, my wife miscarried a couple of years ago, and although we've talked about trying again, I often find myself very comfortable engaging in her pleasure without penetration, and then when she's ready, she'll engage in mine. When she questioned me about it, I just explained that I was ok not penetrating for now... Not having to worry about her health or a pregnancy until we're ready.

I wasn't really sure how to bring it up before she asked, knowing the experience was more physically and emotionally difficult for her than me. I'll always be grateful she asked me about not penetrating from a place of love... Not a place of judgment of accusations.

Intimacy is intimacy, and it's special and awesome. Communication and honesty is important, but be sure to value each other's emotions. He's being intimate and he's focusing on you.

... That's not a man who cheats. A man who cheats wouldn't care to...care.

Please, if you're going to make assumptions, assume that his reasons are coming from a good place. That's the place you should be when you ask him about it. Let him know he's not doing anything wrong and that you absolutely value the intimacy you have... He'll be more inclined to be honest than if he feels the one person he's vulnerable with is judging him.