Here are three things you could do end power struggles and form a longer lasting relationship:
1. The first thing you must do is check that you are inviting the right sort of person into your life - see Incompatible Partner for more help with this issue.
2. As soon as your needs rise to the surface in a new relationship (or you see your partner's needs come up, usually with challenging behaviour) you must stop and avoid any blame of your partner. Instead understand that they are in emotional pain. This is a critical time for your new relationship.
3. Having caught the start of the power struggle, determine to bring the love back to your relationship through your leadership. Start a conversation about what you are feeling and ask your partner what they are feeling. Find out what need is not being met for both of you - it will be the same. Fulfill this need in the best way you can. This will bring the love back and then you will need to look deeper for the causes of the needs and insecurities that come with them.