Cos people can be worms.
I don't necessarily buy this 'make friends with the partner' thing. Really, you should be someone's friend just because you are their friend, no other reason should be neccesary. Not that I am advocating all-out hostility. Do your friends disappear just for the honeymoon stage, then come back? If they do, then I think you may have to cut them a little slack, I'm afraid. But if they disappear for good, with the definition of meeting up being a night out with their partner, then you may well need some new friends, as suggested above. Some people have to totally skewed visions of life and think they have made it because they have found a partner, and state 'I still see my friends' like they expect applause for it. Friends are essential, not some side-dish - if your friends don't feel the same, make some new ones, because you deserve better.