The consequences

Being exploited
If you say yes to everything, people will get used to it and they will abuse your good nature. Once you start taking on extra hours at work, always being the one who makes coffee, organises the end-of-year party and cleans the toilets when the cleaning lady's ill, you're never done being a doormat. The more you give, the more people will take. Why should they bother to do something themselves when you'll do it willingly, after all?!

Being respected
So he wants to see his mates and you've arranged to see some friends. You give in because you love him and you end up making him sandwiches and kissing him goodbye as if nothing's happened. He cheats and you forgive him because you're too scared of being on your own. He loves you, even though you see yourself as the ugly duckling, but all you'll achieve by putting up with this is completely losing your self-respect.