A relationship has to be healthy for both parties to be happy. Some of the characteristics for healthy relationships include co-operation, humor, intimacy, honesty, assertiveness, healthy boundaries, and a willingness to change. These characteristics are possessed by only the emotionally mature. We all know that a relationship requires a combination of time, energy, identity, attachment, finances, extended family and other social relationships. These investments are assets of the relationship. The more you invest into a relationship the greater your chances of profiting and finding happiness. If you've experienced the ill of losing an asset then you'd understand the cost of risking a relationship breakdown after you've put in your all.
Now, if you want to choose the right partner who'd complement you - you need to deal with yourself first; start with your own emotional maturity. Being emotionally mature enables you to heal toxic emotional bonds and accept yourself as you are. Self-acceptance lets you express your emotions. If you avoid your emotions you may become angry, depressed or frustrated. The danger in avoiding or repressing your emotions is that you may unintentionally push your partner away.
When you become emotionally mature you will find your relationship blossoming because in the place of the 'I want it now' attitude is the capacity to face unpleasantness, frustration, discomfort and defeat without complaint or collapse. Emotional maturity permits you and your partner the freedom to pursue your individual interests and friends without restriction. This allowed level of separateness brings lovers closer together. It acts as a bond not a wedge. Partners get to bring their uniqueness into the relationship.