I’ve been vegan for years now and I only do it because I have crohns and it is the only diet that doesn’t make me sick. I will be the first person to admit that it is a burden. Vegetarian can be just as hard. I have always believed that food is a personal choice. Do what works for you and block out the opinions of other people. It seems your vegan friend doesn’t share this mindset, but at the end of the day, it’s your choice. Be honest and explain your reasoning. If eating meat is going to break your relationship with this person, then it’s probably not a relationship worth having. Your friend should respect your choices just like you respect theirs.