Weight Problems

I am currently going through weight issues in my relationship but the only problem is that the person that has an issue with my weight, isn't my boyfriend. It's his dad! I have been with my boyfriend for two and a half years. In those two and a half years, his dad has spoke to me maybe three times. I love my boyfriend to death but I don't know what to do about his dos. I understand I can't please everyone but to not like me because of my weight is a bunch of crap. Especially when I'm not dating him. I'm dating his son. Any advice on how to handle this..? I'm stuck.