Yeah, that song...relationships are flimsy like that...he's saying don't invest so much because everyone is selfishly motivated and the sexes are at war :p
There was this old guy who came from a well-to-do family and his son was an engineer...and he use to come in to where I worked and try to set me up with his son all the time until finally he said 'I just don't get it. Girls use to go for guys with money and now I see beautiful girls like you end up with complete losers.'
I just shrugged and it didn't really hit me until now why that is.
I suppose in some ways we want a bond...something beyond material gain..and there's more to sexual attraction than money...
this is where monogamy comes into play and people believe in 'true love' etc etc
but really...I've learned the hard way that as much as I might love or like someone...that's not going to matter when it comes to me...we have to be selfish...and think about our security and happiness always...