Is Marriage Commitment 50/50?

Marriage is not 50/50. It should always be 100/100.  In the beginning, you may not want to and will test your spouse or wait for them to do 100% first and if they don't, you will step back and do less also. Big, huge mistake.  True love in marriage is committed to 100%.  You give 100% from day 1 and you will be surprised at how grateful they are and will not hesitate to return 100%. When we first realize that we are falling in love, it could be a bit scary at first but with God in your relationship, take a step of faith, one day at time. Imagine how amazing your marriage could be if you both just loved one another and gave your all. Apologizing when you screwed up.  Giving your all to your spouses kids as well as your own. It is possible.
I noticed when we first were married 22 years ago, my husband was somewhat hesitant and I could tell. I knew he loved me but there was some holding back at first.  I gave him all and was there for him and after a small amount of time he began just giving more and more of himself to our relationship.  We both came from a previous marriage that did not end well and beginning a new one could have been more difficult.  Just remember to be sure you are both ready to dive in and dedicate everything to one another when you decide to get married. 
It's not always easy.  Beginning a new marriage with your kids and your spouse and their kids.  Moving in together and getting to know one another.  Understanding each other, building relationships with all the kids in order to maintain peace and joy in your home.  Outside influences are mixed in at a certain level also.  It will take time to build a new foundation of trust. 
First things first.  God and your relationship with HIM is always priority. Then, You and your spouse need to put each other first in your marriage. Support each other.  Then the kids come next, whether they are yours or your spouses.  In this order, you will both know instinctively how important all the kids are because they are your spouses kids and yours, period. Meaning, you love God who brought you together and wants you to love your spouse. You love your spouse so you naturally want to love and care for their kids in the best way you know how. 
Take one day at a time.  Be patient with each other and the kids.   Pray together often.  Trust God to bring you through the tough times and the enjoy the good days.