Knowing all that viewers do at this point about Tyrion - the most likely scenario is one that is much less meme-able but much more in-line with Tyrion's strength: strategizing. Tyrion's reaction might seem strange, especially as he lurks in the shadows outside of Daenerys' door - but the choice to include him here is deliberate and the fact so many viewers picked up on his worried/jealous/sad/angry look means the filmmakers achieved their purpose: call attention to the fact that this new relationship might not be a good thing. In that context, Tyrion's look serves as a foreboding hint toward what is to come. Fans might revel in the King of the North joining with the Mother of Dragons but Tyrion's reluctance signals that a relationship between the two is more complicated than even their (already overtly complicated) familial connections might suggest.
First and foremost, regardless of any feelings Tyrion might have toward Daenerys, professional or otherwise, it's apparent she has been changed by her time with Jon - exemplified by her putting herself, her dragons, and the larger mission (save Westeros) at stake when Jon was in danger during his journey north to capture a wight. Tyrion recognized that act at the time for what it was - reckless - and, the result was Daenerys not only losing one of her children, she subsequently handed the Night King a powerful new weapon to wield (one that he wastes no time in using when he brings down Eastwatch). For that reason, while Tyrion might be glad that Jon and Daenerys had united their armies under a common cause - the lovers' infatuation with each other has begun to create problems in the grander scheme.
Just as Daenerys rushed North to help Jon, Tyrion was equally frustrated when Jon was unwilling to promise Cersei he'd stay in the north - choosing instead to make his oath to Daenerys public to everyone. Again, the gesture was noble (Jon is not an oathbreaker), as Daenerys herself pointed out, but if the goal was to get Cersei on their side, halt aggressions, and defeat the White Walkers, Jon's speech about making promises to only one Queen was a short-sighted and very public display of dedication to Daenerys, not the most tactically sound approach to the team's end-goals.
As a result, it's easy to understand why Tyrion might not be enthusiastic about Jon and Daenerys getting even closer - as their love serves as both a distraction and a point of weakness that their enemies could exploit. It's the same reason Tyrion suggested that Daenerys leave her last lover, Daario Naharis, in Meereen. Tyrion knows the danger of letting love interfere with playing the Game of Thrones first hand - given that his own love, Shae, was repeatedly used as a means by which to control, humiliate, and break his spirits. If you're the chief tactician caught in the middle of a battle on two fronts (an undead army on one side and your estranged sister on the other), the last thing you'd want is the two people in charge of your campaign falling in love - especially given that, before they were romantically involved, they'd already sworn loyalty and focused their attention on a shared goal. If his longterm goal is to defeat the White Walkers and then win Daenerys the Iron Throne, the romance only complicates the situation in the short term - rather than makes Tyrion more likely to succeed in the team's overarching goals.
After all, Daenerys and Jon would not be the first rulers on Game of Thrones to have let love cloud their judgment with lethal consequences (R.I.P. Robb Stark and Tommen Lannister). While the pair might be enjoying their new-found relationship, the romance is likely to hit any number of hurdles in season 8 - and, even if it'd be great to see a happy ending for Jon and Daenerys, Game of Thrones isn't known for happy endings. A much more likely scenario would see Daenerys sacrifice herself, and all that Tyrion has attempted to build, in order to save Jon - which is why, more likely than not, that Tyrion does not look pleased on that boat.