Sam (Colin Firth) and Tusker (Stanley Tucci) have been together 20 years, and they bicker like an old married couple. But there is obviously love, not anger, in their debates, such as whether or not to use the navigation system in the RV they are driving across England.

Written and directed by Harry Macqueen, the poignant “Supernova,” which will show at area theaters on January 29 and at home on-demand on February 16, shows how Sam and Tusker’s love is challenged during a critical time. Tusker has dementia, and while Sam has been caring for him for two years, life as they know it (and knew it) is becoming more difficult. 

Macqueen, thankfully, does not succumb to too much hand wringing with this melodramatic material. Nor do the fine actors, who mostly exercise restraint in their performances as they create the dynamic between these two men in love. Sure, Sam does take to excusing himself to the bathroom to have a cry, blaming his tears on the onions he is chopping, and Tusker pretends to forget someone’s name (a tired dementia joke), but these are predictable lapses. 

“Supernova” slowly reveals where these characters are going on their road trip. It is not just to Sam’s sister Lilly’s (Pippa Haywood) house for a surprise party, nor is it to a recital Sam, a noted pianist, is planning to give. As Sam discovers in a contrived scene in which he snoops through Tusker’s stuff, his partner is planning to end his life to spare himself — and Sam — further suffering.

The decision is not unexpected. Early in the film, Tusker explains that he deliberately did not bring his pills because he did not think they were effective. But for Sam, who wants to spend every moment he can with Tusker, the decision is devastating. In one of the film’s more thoughtful moments, someone observes that people should not be mourned while they are still alive.

“Supernova” is best when it makes points (or platitudes) like these. The idea of taking one’s life or assisted suicide is not the issue here. The film is more focused on the idea Tusker expresses, “If you love me, you will let me go.” Tusker does make a strong point when he complains about losing control and being more of a “passenger” in his own life. However, the impact of Tusker slipping away is perhaps more difficult for Sam, the survivor. To the film’s credit, Firth makes Sam’s fear and despair palpable even as he seethes quietly.

Unfortunately, “Supernova” only scratches at the surface of which is worse: being the caregiver, or the one who needs the care? Both partners suffer differently, and yet they both selfishly want the other to bend to their wishes. Macqueen should have dug deeper into this very real dilemma. Instead, the characters have conversations about moving to a new, easier home, hiring someone to assist Tusker, or making plans for the future that come off as ticking boxes and dismissing the points that should be addressed shortly after a terminal diagnosis, not two years later. 

“Supernova” often goes for sentiment, not sensibility. This is why Tusker gets a cringe-inducing speech during one of his lucid moments where he prattles on about the stars and how one’s ears could be made up of materials from two completely different galaxies. Likewise, when Sam and Tusker tape record their conversations for posterity, it comes across as forced whimsy and telegraphs the big reveal.

These scenes needlessly lard the film and may be why the compelling moments are so few and far between. Much of “Supernova’ feels slight. This may be the point — that boring domesticity is desirable, because when the tectonic plates shift, nothing is ever the same again. Yet this approach simply delays the more interesting part of the story, and reduces, rather than enhances any emotional connection. Sam may cry for Tusker, and there are some touching moments —a speech Tusker wrote where he reflects back on his life that Sam reads aloud is quite moving — but this film does not jerk many tears.

 “Supernova” is most sensitive when it showcases tender, affectionate scenes, such as Sam rubbing Tusker’s arm in bed, which makes him fall asleep, or Sam helping Tusker button his shirt. But other moments that are meant to amuse or disturb — the men sharing a single bed, or when Tusker briefly goes missing, respectively, fall flat. 

 Firth and Tucci both give earnest, heartfelt performances that elevate the material, which often feels stagy, or a step above a TV Movie. And while both actors, who have played gay roles throughout their careers, are convincing as a couple, one might speculate about how the film might have played if out gay actors portrayed Sam and Tusker instead. Firth and Tucci never disappear into their roles, which can be distracting. 

“Supernova” is not without merit, but this well-intentioned film never transcends its flaws.