My fianc�'s starsign isn't compatible with mine!!?

Last week my boyfriend proposed to me. Obviously I said yes because I didn't want to embarrass him in front of everybody in the restaurant. I am a Pisces and he is a Sagittarius which I've read is a really bad match. I'm seriously considering dumping him. How should I go about it? 'I know we have a baby and are engaged but our starsigns don't work well together so I'm leaving you'??