My advice is going to sound strange and you may or may not want to take it, but here it is.
Read smut and practice writing smut.
Yes, read a truckload of really, really well written smut. Why? Because no other scenes will ever stretch you as thin as smut and a writer who really knows how to write them can (and must be able to) make readers salivate and shiver at the sight of a button being undone.
Once you’ve learned how to write smut you can apply the skill to all kinds of tension. A well-written smut teaches you to focus on the character’s emotions, reactions, body parts, and expressions and how to use them to bring about tension. What you need to make your readers root for your couple is small, classy touches of foreplay that builds up gradually to the climax. It doesn’t have to be physical. Smut writers can stir up your emotions with the simplest act of eating an apple or drinking coffee. You’ll learn how to make one look powerful enough to trip a person, to make pauses and punctuations that solidify the air in readers’ lungs, that sort of thing. I’ve used the smut writing technique to create tension for political meetings even, and it works amazingly.
In smut you will read or write:
He pins her down to the bed with his eyes as he draws nearer. His hand slips out of his pocket and reaches for her, pausing just above her button for a moment, lingering there, deciding when and how he would undo it. She holds her breath as she watches, hear heart pounding against her ribs imagining the moment his finger touches her blouse. Etc.
In a meeting you’ll learn to write:
Silence fills the room as he walks in. His footsteps firm and precise, demanding absolute attention from the entire room of twelve men who straightened abruptly in his presence. He sits, in a deliberately slow manner, and waits for his coffee to be filled before he reaches for the paper. His finger rubs back and forth along the sheet as he reads, and then it stops, and twelve beating hearts stop with it.
It’s an unconventional advice but I’ve learned so much from reading and exercising writing smut. I hope that helps.