Disclaimer: I'm rehashing a lot of old RP theory, but I felt compelled to share how everything finally clicked for me.
Summary: Don't be swayed by a woman pledging her eternal love to you, because it is an (allegedly) enduring promise made by a creature that lives in the moment.
Body: I was lying in bed with the ltr on a relaxing Saturday morning. She rolled over, looked me dead in the eye, said "I want to spend the rest of my life with you," and I felt..... nothing and then surprise at my apathy. You see, something clicked that every moment. The last little bit of the bitter pill had be dissolved by my formerly blue pill stomach acid.
I realized that very moment that her want of commitment is identical to my want of sex. It is automatic. Hearing her say those words evoked the same response from me that I would get from hearing my buddy say "man, I want to fuck that girl." That response is: no shit.
This is not to say that everything a woman says is a lie. This is to say that he pledge of fidelity, or rather her want of fidelity, she gives to you is because of how she feels for you right then. When those feelings are gone, the promise no longer makes sense.
Finally, as a side note, Your commitment is what she is chasing, not what she's selling. Within the confines of a ltr, that is your leverage. Don't let someone try and pay you with your coin.
-Women don't give commitment, they seek commitment
-Women's want of commitment is like your want of sex
-Commitment is yours to give, not to chase