YOu have already talked to him and it makes him colder and withdraw.
Okay, and well gut instincts do occur... and pregnancy hormones do tweak a woman.
Maybe, he is having a hard time dealing with a pregnancy too. Have you asked him? Do you both talk about it and your pregnancy? Its HIS pregnancy too... not only yours. For some men, it freaks them out. Or makes them feel older and not attractive anymore, or creates insecurities or anxiety in them.
You both need to talk about your pregnancy... and about the upcoming baby. HE needs to be included in that too. Does he go to pre-natal visits with you? It would be a good idea. And shop for baby together. Set up the house for baby together etc. Do ANYTHING together...
Next, a guy looks at other women. They are men. It does not stop just because they are married or have kids. Even the most genuine nerdy guy Husband will look at other women. So... either he must be authentic about it and tell you... or he acts like its the biggest SIN in the world and pretend he's a Monk and lie about it to you.
Or... he really is cheating. Which, you will either get an honest answer... or you won't.
My Hubby, gets all kind of business cards at work... from women as well, with their numbers. He tells me. Its nothing abnormal or nothing to hide. So what. I am not threatened by it. He has female friends too. I have guy friends. No biggie. So there are normal things like this... or there are abnormal opposite sex interactions, that are about cheating.
The thing is, you don't have a bottom-line answer... and you already asked him. He either feels you don't trust him so he withdraws.... or he truly is guilty.
All the best,
Susan