Oracle SQL social network queries?

I am working on small relational database queries for school. I have tried several things but these queries aren't working out for me. I can paste what I tried for every one but suggestions are more than welcome at this point as time is running out.

Table: Users

Attributes: Id_pk, Name, Gender

Table: Friends

Attributes: Id1_pk (fk to users.id), Id2_pk (fk to users.id),Startdate

Table: Comments

Attributes: CommentID_pk, Poster (fk to users.id), Recipient (fk to users.id), Text, PostDate

I am currently working on a query to show all pairs of males and females who are friends since this year. So far I am trying this:

Select *

from users a, users b, friends

where id1 = a.id and a.gender = 'M' and id2 = b.id and b.gender = 'F';

intersect

Select *

from users a, users b, friends

where id2 = a.id and a.gender = 'M' and id1 = b.id and b.gender = 'F';

I am trying to form a query that makes sure they are of opposite gender with matching ID's.