Friends ex

Ive been friends with a girl for about 5 months and i’ve been talking to the boy she dated just under 2 years ago for about 10 months i believe. My friend is now in a happy relationship with someone she adores, are exes always off limits? I really get along with this boy so just thought id ask some opinions :( we went to the same secondary school and we are in college now but i wasn’t friends with either of them during their relationship.