The key is not so much about deep friendships, it is about interaction with the opposite sex.
So, you don't have to build a strong friendship with a female friend.
All you have to do is even though you are in a relationship, you still keep interacting with other women:
- Flirt a bit.
- Chat with a girl you just met.
- Activate your social power when attending an event.
- Etc.
Once you realize that other women like you too, your level of power and confidence is REALLY boosted.
When you rely only on your girlfriend or wife for female validation, this makes you very dependent on her.
The moment she transfers a bit of her attention to another guy, even if it is for a couple of hours and there is for sure nothing going on, you still feel insecure and left out because she is all you have.
Now, if the moment she comes back home, she sees you on facebook chatting with an old female friend who just found you back, the balance is shifted instantly!
Let's get this right, ok?
The goal here is not to make her jealous. The goal is to have other sources of social validation in your life, not just your partner.
That's the key!