What does this expression mean?

[Traceey]

I can't even find it on google. But I heard my friend say he can't hang out with his friend and these girls he invited over and then he said 'that relationship tag really hurts'. What does this mean? I didn't really get it. I know he has a girlfriend but it still doesn't make sense.

[Liz]

It means that because he is in a relationship , his girlfriend would not want him having fun with his friend and with other girls because she would get jealous .

[Olgha]

Maybe she indicated on a social media network (Facebook or any other) that she's in a relationship with him. When a person clicks on the "relationship tag" on something like Facebook, it shows everyone on their friend list that "A" is in a relationship with "B". It shows this information on both their profiles.
If she did this, it therefore means he can't hang out with other girls or party as he likes coz well, everyone knows he's in a relationship.

[b]

he just means she isn't really his girl friend, just an acquanitance