Best Answer - Chosen by Voting
Usually, the difference can be fixed through what is written around "friend"... If somebody says "mein Freund" or "meine Freundin" you can be relatively sure that she/he is speaking about her/his boy/girlfriend. Otherwise one would say "ein Freund" or "eine Freundin". But obviously using "mein" can only a give a first indication which might not always be true. You have to listen a bit between the lines. And if you are insecure why not just asking? In case you do not want to leave any doubts whatsoever you say "mein Partner" or "meine Partnerin", respectively.
Beispiel:
Ich treffe mich nachher mit meinem Freund. (Meet the boyfriend...)
Ich treffe mich nachher mit einem guten Freund. (Meet a good friend...)
