If you want your mum to be happy, you'll just have to find a way, maybe spend some time with him and find some common ground.
Edit: Is it him or is it that your mum is spending less time with you and you feel left out, if that is the case you need to let her know how you feel. Keep in mind you both love her.
Edit: Is it him or is it that your mum is spending less time with you and you feel left out, if that is the case you need to let her know how you feel. Keep in mind you both love her.