Jenny would rather watch cricket than stomach Tim's mum's cooking
You really don't feel like going to his mum's for the weekend to play Scrabble, flick through photos of your boyfriend when he was 5 and listen to her criticize your taste in clothes, food, music, and...pretty much everything, apart from your taste in men.
> How not to act
Since you can't actually say what's on your mind (otherwise all hell will break loose), you change the way the conservation is heading and try a bit of emotional blackmail: "You know full well that your mum doesn't like me (implication: whereas I do all I can to get on with her). If you love me, you won't make me go though that..." You think making him feel guilty will make him give in, but you're in for a cruel disappointment...