What's the best way to convince my son to end his interracial relationship?

My son is in love with his african girlfriend and he wants to marry her. I met her and she's very nice and smart. My son recently had to move to sweden for a 6-month contract and before he left, he was very sad to be away from his girlfriend so I told him that he could meet a nice swedish girl and he got mad. I'm not racist but I think it's better to stick to your own race. Since I made this comment, my son has been ignoring me and his girlfriend called me a bigot. I am very hurt by her reaction because we welcomed her into our family and I believe it's our right to prefer if our son dated a white girl. My son now wants nothing to do with me and I'm sure his girlfriend is the one manipulating him. How can I convince him to end this relationship because it's for his own good.