Resentment can cause stress and anxiety, even depression so it is from the outset a very unhealthy feeling to hold.
As a Stepmother the feeling of resentment can manifest itself for a number of reasons. The common reasons are:
~ The time that your new family revolves around someone elses child.
~ The 'invasion' of your home when it is your partners visitation.
~ The cost and money taken from your household.
Initially you may feel resentment towards the child, but in realistic terms its resentment of the situation.
Suggestion to Help Deal with your feeling of Resentment:
Write it down.
Take a piece of paper and write down ALL the things that cause you to feel resentful.
You can make it as detailed as you like.
Now re-read it several times.
Ask yourself these questions. Are they really that important? What can I do to change them? Then look at who or what the majority are centred around. If it is one person (say stepkid) then ask yourself what can that person do to stop me resenting them?
More likely than not, with a stepchild, there won't be much they can do. They did not create this situation, nor did they ask to be born into it.
You may find you feel less resentment and feel better in yourself.