What do I do if my boyfriend keeps on insisting to visit her mother when he's out of the country? I already asked his mother if I could come over but she insisted that it's better if we talk via sms.

Have you explained to your boyfriend about his mother's feedback? It is best to talk to your boyfriend about it because his mother might take it negatively if you still visit her even if she said no. Also assure your boyfriend that it's not thay you don't want to do it, but you are thinking of what his mother might feel if you (boyfriend and you) insisted on visiting.