Wolfwood has an awesome collection of links on this subject matter. Hope he jumps in some time.
I'm specializing on long term multiple sexual relationships. Just remember that when a girl is saying, "I love you," that's actually girly speake for: "I want your cock inside my pussy every night." She is not actually in 'love' with you. The girl is just horny.
Now, if she's saying things like, "I can't live without you." or "I think I won't be able to live if I found out you have other women in your life" or some stupid shit like those, then the best way to handle those is to kill the attraction. When a girl is saying stupid shit like these, what she really means is: "I love you." Kill the attraction fast when you've reached this point.
That's a smoother exit strategy. But it takes time though. How? Act AFC and needy around the girl. She'll fall out of love in no time.
Field tested.

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Approach. Open. Escalate. Isolate
Here are my two essential rules on texting that will save you tons of time and money:
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