So, if I understand correctly, when you’re on a single post page, you want to have a navigation menu with all the posts of post_type bbp_forum.
I had a similar case (without the post_type, but it’s not a problem to add it), and I used code that I found that talked about posts of same category, on single post pages.
The code goes as follows (with customization for post_type):
<ul>
<?php global $post; $cat_posts = get_posts('post_type=bbp_forum');
foreach($cat_posts as $post) : ?>
<li <?php if($post->ID == get_the_ID()){ ?>class="cur_post" <?php } ?>>
<a href="https://wordpress.stackexchange.com/questions/11886/<?php the_permalink(); ?>" title="<?php printf( esc_attr__( 'Permalink to %s', 'twentyten' ), the_title_attribute( 'echo=0' ) ); rel="bookmark"?>" ><?php the_title(); ?></a>
</li>
<?php endforeach; ?>
</ul>
I hope that’s what you meant.
P.S – I also see that you have an opening <ul> tag, but a closing <div> tag….