How do I deal with the jealousy of my step-son and wife's relationship?

My wife and I have just recently been married a few months ago. We were each married before and have one child from our previous marriages. My wife however is not a wretch of a woman and knows that no matter how much she can't stand her ex, she was never going to use her son as a tool to get back at him, and thus they share custody 50-50. I however have a long distance relationship with my daughter. I have her in the summer and just one weekend a year. There are many times when I get rather depressed and saddened when I see the two of them together and I feel like the odd one out, and it makes the amount that I miss my daughter so much larger. My wife knows this and thus I feel horrible in the fact that I am also negatively impacting their relationship. She still mentions it, but I know that nights when her son is not at our house, and she does miss him, she doesn't mention it as much anymore as I got angry one time and said that she she try walking in my shoes. I never felt this way before, but now that we are around one another twenty four seven it it makes it so much more noticable.