Humans, dwarves and Qunari don't have the heart icon/flirts with Solas either, even females. IIRC male characters can't flirt with Blackwall, either. I could be wrong, since I've only played as elven females, but that is what I read elsewhere.
This would indicate (to me, anyway) that despite dialogue for male characters existing for Solas, he was probably never actually intended to be anything but straight--just as I'm pretty sure Blackwall was always intended to be straight (he was going to be THE straight option for women, in fact, with Iron Bull being the pansexual option everyone could pursue).
Now, beyond "it's just because he's only into women," which makes sense from a real-human standpoint... Solas is a character. There were "super story reasons" for him being so heavily gated, and I continue to wonder if those "super story reasons" haven't all come up yet. I get why he is elf-only, with what little we know of his backstory and with the vallaslin thing. But what if he had to be straight for story reasons, too, and we just don't know it yet? I mean the obvious alternative is "he's just straight," which is... a perfectly valid reason, and perfectly okay. Again I don't need justification for his being straight (and yet part of me feels I should be more aggressive on that point for the LGBT community's sake, but yet it just feels wrong to be that way, since I don't ask for justification for Dorian being gay?)... but he's a character, and characters are written certain ways for reasons, usually.
I continue to wonder if there's an optional god-baby in the future, which is something that wouldn't be possible for a male Lavellan. I would totally be okay with that even though I normally dislike pregnancy plots, as long as it's optional and declining doesn't hurt one's relationship with Solas... I just think it'd be a neat little wrap-up to the romance, perhaps available in the final DLC so we don't get to see the pregnancy/baby/etc. until next game, when we are no longer the Inquisitor.
To me, Inquisition felt a bit incomplete, main story wise (It has lots of side story to fill the gaps, to be sure, but its main story is very small). I can't help but feel that we're going to get a whole lot of DLC, and that we may see a longer-than-normal gap between this game and the next one.
Also, remembering that originally our choices would have been Blackwall or Iron Bull, I kind of wish I had twitter to thank the devs again for giving us Solas and Cullen.
Edited for clarification: I kind of feel like I'm in the wrong for not needing specific reasons for Solas to be straight (I'm curious if there are extra reasons, but I don't NEED any reason other than "he's straight"), even though I know I'm not wrong to be okay with it... it's a confusing thing to feel. It's just that I feel bad for other people who don't happen to be straight women, or like playing straight women in games, and I wonder if I should feel worse/fight harder for them?