It's little things like this that make it hard for me to believe Solas and Lavellan never had sex. It's like he pretends to have his indomitable self control...except he loses control in battle (lighting his breeches on fire), getting tipsy at Halamshiral, at the mages who killed his spirit friend (don't blame him for being pissed, just saying), every time you touch him he can't help but kiss you...etcetera. I mean, my Lavellan wouldn't have kept her hands to herself for that long and I can't imagine he could help himself. And yet the story does seem to indicate they never actually got it on,though it is slightly open to interpretation. IMO
I don't think that's entirely fair. My boyfriend kisses me passionately, grabs my butt and cuddles/snuggles close every time I give him half a chance, but we've never had sex. He knows I'm fearful of sex and is really sensitive to my reactions. If I show the least bit of hesitation or pull away, he asks if I'm okay and/or eases up. He's also used to delaying perssonal gratification (he can go 72 without eating without feeling too bothered or close to 24 hours without sleeping if he's really busy, and sleeps only 4 -6 hours on average anyway.) Imagine an immortal god who is so intuned with the world (the Fade, spirits, memories, emotions, and magic connected to it) and whose people "lived at a pace that sustained ourselves for ages."
Solas does kiss Lavellan very passionately every chance he gets, but only after Lavellan makes it clear she's ready and willing (her kissing him in the Fade, her assuming a coy, girlish flirt pose in anticipation of another kiss on the balcony and then whispering, "Don't go" when he turns away, them sharing a mutually loving moment in Crestwood), and he pulls back every time. No matter how intense, Solas makes it clear he can and will pull away any time.
I think this is where personal imagination and our perceived Lavellan comes in. If you picture her being just as eager or desiring to do... the deed... then I think Solas would be all over her like hot fudge on a sundae. I think that if she didn't want to and/or showed any hint of fear, nervousness, or hesitation, he would pull back, go at a pace she was comfortable with, and make it clear "only when you're ready."
I personally have no problem imagining they didn't do it, because I picture my Lavellan being fearful, nervous, and hesitant at the prospect of sex, and I simply can't see Solas pushing her or overwhelming her with passion if she wasn't ready. But, that's just my interpretation. If you can see your Lavellan responding differently, more power to you. That's why there are just as many hints that they did do it as hints that they didn't.