The better half...

Ideally your better half is someone who completes you (literally!). He/she should like the part of you that you yourself cannot stand. They should admire the qualities that you are not even aware exist. They should complete the process of loving yourself for who you are. This was actually quite well thought-out. The intention was to ensure that each and every one of us is loved unconditionally. Hence, we are destined to pair up with the person that helps us complete the "Circle of love"...Hence the term "soulmate" (he/ she completes your soul).
Now, your twin soul would then be someone who is just like you - in that they love the things about you that you also like. This makes sure we all have and maintain our self-esteem and are confident of our capabilities...:)