The shiny new drama Fellow Travelers glides through all the major markers of prestige television. Glossy production values, multiple timelines, a combination of sweeping score and expensive needle drops – it’s almost appointment viewing by numbers, carefully ticking boxes we’ve seen ticked to exhaustion over the last two decades. But within the first 10 minutes of the opening episode, we also see something that’s notably less familiar, if not absent, even in the expansive bloat of streaming TV: explicit gay sex.

It’s surprising to find it outside of more niche queer content, but especially so in a show that is otherwise rather too polite in its posture and politics – a Sunday night romance designed to appeal to a straight mom-and-pop audience. The sex scenes are both jaw-droppingly graphic and crucial to the plot, a convincing riposte to the recent argument posed by puritans that watching actors simulate sex is not just morally dubious but unnecessary. Throughout the eight episodes, which span almost 40 years, a tragic love affair is given much needed texture via sex, and it is the most intriguingly transgressive element of a series that could have benefited from taking a few more risks.

Based on the 2007 novel by Thomas Mallon, Fellow Travelers is a story of fictional characters making their way through real events, starting in the early 50s and ending in the late 80s, from Washington DC to Fire Island to San Francisco. Hawk (Matt Bomer) and Tim (Jonathan Bailey) meet on opposite sides of the political divide as McCarthyism eats up the world around them, turning paranoid colleagues against each other. After an unspoken initial attraction, their dangerous flirtation turns into an illicit tryst at a time when McCarthy and his cronies were grouping communists together with so-called deviants – a witch-hunt that pushes them even further back in the closet.

The narrative switches between their early, heady days and the sting of what is to come, as Tim is dying of Aids and Hawk is trying to sustain a marriage with a forced childhood sweetheart (an underused Allison Williams). It’s a stretch for even the most committed actor and talented makeup artist to convincingly portray the same character over many decades, and one of the show’s hokiest touches is the handsome actors given neck wrinkles and the odd liver spot. But the sight of poorly aged thirty- and fortysomethings in their fake 60s dealing with gravely important issues sums up the show’s dissonance – a political period drama based on real, difficult history but told with the broad brush strokes of a soap opera. Once the viewer has got on-board with that tone, there are pleasures to be had here, far more than in last year’s heinous adaptation of 50s-set gay romance My Policeman, which also boasted some of the same team, including the Oscar-nominated Philadelphia writer Ron Nyswaner and the producer Robbie Rogers.

Fellow Travelers is an infinitely more successful attempt to tell a similarly impossible behind-closed-doors romance. It is lushly lit and at times stunningly cinematic, with the kind of intricately designed period recreation usually saved for the big screen and the all-encompassing romance usually saved for straight stories. It is only affecting in part though, with the soapiness robbing some vital moments of their power. The dialogue can be inelegant, and the pair’s back-and-forth romance goes from repetitive to confusing as the timeline gets muddied in the last few episodes. But there’s an outstanding performance from Bomer, the kind of comically handsome leading man who would have been a household name by now were he not openly queer in real life. He’s not quite matched by a slightly less certain Bailey although the two have an easy, sexy chemistry, both with and without clothes.

The sex between the pair is the most interesting and unexpected ingredient here; Nyswaner understands how profoundly important their private moments are in a world where they cannot be themselves in public. There’s a dom/sub power dynamic that’s explored without the need to smooth down its edges for a wider audience and it is smartly maintained even as their feelings deepen. This is a show that realises kinky sex can be accompanied by woozy romance. As the latest in an increasing line of series and films that try to push gay love from the outskirts into the spotlight, it is one of the less sanitised examples. There’s also a less explicit but often more moving relationship running concurrently, between Noah J Ricketts’s drag-wearing performer and Jelani Alladin’s journalist fighting homophobia and racism; a scene between the pair provides one of the biggest lump-in-the-throat moments.

With eight hour-long episodes trying to retell three decades of events, Fellow Travelers is both overstuffed and underwritten, its admirable historical scope often leaving little space for the characters to breathe. You’ll be with them until journey’s end, but you’ll wish they took fewer detours.

• Fellow Travelers airs on Showtime in the US on Sundays and is available on Paramount+