Very good question!
There are really three kinds of 'strains' that any person can follow, depending on a few things.
The strains are family members, males, and females.
Male friends have a couple of stages.
There's acquaintance, where I know of you, we've talked a few times... maybe we are in the same class together, and have passed a piece of paper to each other or something. There's no real trust, or connection built between us.
Then there are friends. We interact more frequently. Maybe you're a friend of one of my friends, and ipso facto you're my friend. We occasionally do things together, and are learning about each other. I might stop and say hello to you when you walk by. I wouldn't trust you enough to do anything but common, courteous things.
Then there are good friends. We interact daily, work on assignments together, or work together. We know a lot about each other, and there is some level of trust between us. There's mutual respect. I would say hello to you if I saw you, for sure. I trust you enough to lend you one of my most valuable possessions, such as books.
Then there are best friends. We are constantly talking to each other via text message, planning events together. We know all about each other, and have inside jokes. You get to see the 'real' me. Iceman melts. I would wake up in the middle of the night to save you if your car breaks down.
For females, it's largely the same as for the males, but there's a stage that ranges from good friends to best friends. It's called the girlfriend stage. The major difference? You get to have sex with me. You get to see my emotional side. (The MOST valuable thing to me. MUCH much greater than my books.)
Then there's the wife stage above it, but I haven't explored that stage. So, I can't really tell you about it. I imagine it's like the girlfriend stage, and the family stage mixed together. I am sure this will become very important to me when it happens.
Family... I do anything for them. They see the real me, and can read it. It's very hard to describe. It's the most important stage of all.
I'm sure there is another stage for my kids, and my brother's kids, but I haven't any experience with that either. I am sure they will be up at the top of the ladder, though.
Hmm... That's all I have for now. Hope this helps.