TL;DR
Find out why she's uncomfortable with having your son around with non violent communication
Make it clear your son is important to you and that you want him to be part of your life, and that it doesn't mean you'll go back with your former spouse or leave her
Make sure she feels loved by finding out about her preferred love language and practicing it to express your love to her
My parents broke up shortly after I was born. A little while later, my mother found out that my father was in a relationship with two different women at the same time, and I happen to have twin siblings my age. Although my mother learned early on, my siblings' mother was told about my existence nearly two years after I was born; she thought my mother was just a friend of my father's. She immediately urged him to burn every bridge with us. I haven't seen my father since and they never told their children they had a sibling from a former relationship.
It's possible that your wife may feel frightened by your previous marriage. His existence might remind her of your former relationship and she may be afraid you'll have regrets. I know it sounds irrational because you're only willing to see your son and not your former spouse, but if she feels the same way my "mother-in-law" feels, that's likely what's happening. Therefore, what you might want to do is to reassure her about your aim, which is to keep a connection with your child.
The best way to convey this aim, in my opinion, is through non-violent communication. You might want to initiate a conversation in which you calmly tell her you'd like to discuss the fact that she seems like she doesn't want your son to be around, and you struggle to understand why. Keep it non-judgmental, as it's the best way to make her talk about what is bothering her. Something along the lines of:
Hey Ana, there's something I'd like to talk to you about. I have the feeling you have been uncomfortable with me mentioning my son or wanting to have him around for a while. I feel sad because you're both very important to me and I wouldn't want to lose any of you two. I'd like to understand if my feelings are true and if so, why is it you're uncomfortable with him being a part of my life?
should trigger a conversation in which she'd likely tell why she's bothered and outlines the fact that he's important to you and that you want him to be a part of your life.
She might answer something that may look like jealousy or fear of losing you. Even if she doesn't, I think it's important for you to reassure her on the fact that she is the one you chose to be your wife and that you're not planning on replacing her or making her feel being left behind. A way to make her feel reassured is loved is to use her preferred love language and do things accordingly which will make her feel loved and confident about your faithfulness. If her love languages is gifts, you may want to give her something she's been talking about buying/acquiring for a while, if she prefers touching, make sure to hug her and cuddle on a regular basis. This will help reassure her that she won't be left behind on your way to deepen the connection with your child.
