You feel it, literally
This is obvious but hard to explain. When you have one-sided attraction, though you like them, if they were to talk to you, you wouldn’t feel an electric shock go through your body. But if it’s mutual, you feel something like an electric shock. You feel it in your stomach, chest and genitals.
The energy changes when you’re together
You can be with your friends but the minute he walks into the room or he approaches you, the energy switches. If you’re sexually attracted to each other, you feel the shift from friendly into sexual.
Sexual tension isn’t something only you and that person feels. People around you can also feel it. When two people are into each other, it’s not hard to see or feel it. If no one comments on you two, well, either everyone avoids the subject or no one feels the sexual tension.
Eye contact is intense
You have moments when someone looks at you and then you have those moments when they “look” at you. Yeah, that look, that’s the one. If they can’t take their eyes off of you and if they do, they’re ‘paralysed’ for a moment, they want you and look like they want to ravage your entire body. That’s sexual tension right there.
You flirt a lot
Flirting is all about sexual tension. When you flirt with someone, you basically build sexual tension. Now, if it’s just you flirting and they’re not responding, this is a one-sided attraction. However, if you flirt with them and they flirt back, well, they’re into you, at least on a sexual level.