No, it’s not “new math”, it’s God’s marriage math.
“For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh” [Mt 19:5 NKJV]
While I certainly see a sexual component in this (in 1 Cor 6:15-16 Paul says that having sex with a prostitute makes a man “one body” with her) it is so much more. When we marry, God wants us to lose who we are. Both husband and wife should change, becoming something different than either was alone.
Does this mean you each give up half of who you are? I don’t think so – this is certainly a case of the whole being greater than the sum of parts. What’s more, the whole can be things that neither of the parts were and do things neither was able to do.
Can I explain it? No, not even close. But I have experienced it in my marriage, and seen it in the marriages of others. In a good marriage, both individuals are better and more capable than they would ever be separate. If you are not seeing that in your marriage, I suggest focusing on your marriage and making it a top priority.