Another option I'll suggest is that he might be bi and not really sure how to discuss that.
I was 15 when I realized that I was gay. Then, at 16 I fell in love with a guy (I'm female) and got really confused. I was in relationship with him for more than 4 years and people kept referring to me as straight. I knew that wasn't right, but, I couldn't figure out how to correct things -- or even what the right correction was.
I was 26 by the time I really came to terms with the idea that being bi doesn't have to mean that I'm attracted to both genders in the same way or that I'm attracted to all types of people (I actually have quite a type in each gender and they aren't the same). There's also a fair bit of societal pressure for bi people to ignore the same-sex part of their attractions and a societal stereotype that bi people aren't any good at monogamy. (I am hopelessly monogamous, so, I never felt like I belonged.)
So, at 26, I finally understood myself to be bi and was ready to accept it and claim it. Ironically, I came out to my family at "gay" at that point because it was still easier than telling them that I was bi and arguing against the possible pressure to just "choose appropriately". I figured the bi part would come out on its own when needed. But, I married a woman a few years later. So, unless something catastrophic happens in my life they may never figure it out.
So, it took me 11-12 years from the point at which I was first certain to get to the point where I was certain enough to label myself with my family. It wasn't so much because I doubted them (at least not all of them), but, because I just didn't really know what to say.
As for movies:
Two of my favourites are "Get Real" and "Beautiful Thing"
- They are both British and pretty serious explorations of the difficulties that teenagers face. You might want want to watch them yourself first so that you will be prepared for discussion.
- These aren't easy movies, but, they have a lot of emotional energy and do a beautiful job of illustrating how the world can be difficult and yet also more accepting than you expected.
Milk
- Is the story of Harvey Milk and his fight for gay rights as he became the California's first openly gay elected official.
Latter Days
- Is a fun intersection of the stereotypical "gay lifestyle" that so many people want to believe is reality and the stereotypical Mormon church.
- It's rough, but, ends happily.
- If you watch this, watch the special features on the DVD as well. The main writer is gay and grew up in the Mormon church. He says some good things about why he wrote the movie.
If he likes Science Fiction, I'd recommend the Torchwood series.
- It's much more subtle, but, it also does a good job of illustrating that the gender of your partner doesn't have to change the type of relationship that is possible.
- To get the full storyline that I'm thinking of you'd need to watch Doctor Who Season 2, Torchwood Season 1, Doctor Who Season 4, Torchwood Season 2, Doctor Who Season 5 (a bunch of specials as David Tennent leaves the role), (listen to) 4 BBC radio Torchwood Special Episodes, Torchwood Season 3.
- But, Torchwood by itself tells the story reasonably well.
- I will warn you, Doctor Who is for all ages and is considered Children's television. Torchwood is television written for adults and is much more serious in nature and doesn't gloss over or ignore sexuality.