You and your friend like the same girl

If your friend likes the same girl you do, a common piece of advice, and a sensible one, is to tell him the truth early, in person, before either of you has done anything. In many versions of this, secrecy ends up hurting more than the attraction itself.

Two people liking the same person is common, especially in a shared friend group, class or team. It's awkward, and it can be handled without losing the friendship.

First, sort out which situation you're in

The right move depends on the facts, so check them before you decide anything:

Neither of you has said anything to her. The simplest case, and the one with the most freedom.
He said it first, or called "dibs." He told you before you spoke up, or claimed her.
He's already seeing her, or he went on a date. Then the decision has already been made by the two of them, and the respectful move is to leave it alone.
You've been seeing her and he just told you he likes her. Now he needs to hear it from you.
Neither of you knows if she's interested in either. She might like neither of you.

That last point is easy to forget. You and your friend are both guessing about her feelings. The whole argument could be over someone who sees you both as friends.

Why "dibs" doesn't work

People use dibs as a shorthand for "I said it first, so back off." It's usually said with good intentions. But it has a built-in problem: the person it's about never agreed to it. She isn't a prize that one of you can reserve. She picks, or she doesn't, and that choice belongs to her.

That doesn't mean timing and loyalty are meaningless. It means a better question than "who called it first?" is "what would each of us be okay with, and what would we regret?" Those are things you can actually talk about.

Talk to him

Do it in person, soon, and keep it low-pressure. Not over the group chat and not when others are around.

You could say:

"I want to tell you something before it gets weird. I think I'm into [name] too. I didn't want you to find out another way. How do you feel about it?"

Or, if he's the one who's told you:

"Thanks for telling me. I'll be honest: I like her too. I don't want this to wreck anything between us. Can we figure out what's fair?"

Then listen. He may be hurt, relieved, annoyed, or indifferent. Let him react. Don't defend yourself in the first minute, and don't make a case for why you deserve a shot more. You're after an honest conversation, not a ruling.

Your realistic options

There isn't one right answer. Each has real costs, and the choice is yours.

Option 1: Step back

You decide he matters more than the possibility. Maybe the friendship is closer, or his feelings are stronger, or you've only just noticed yours. This protects the friendship, and it can cost you a chance you'll keep wondering about. It works best if you really mean it, and not if you'll resent him in two months. Don't step back and then quietly sulk.

Option 2: Both go for it, openly

You each know the other is interested, you each get the chance to talk to her, and you agree to some ground rules. Reasonable ones might be:

No talking each other down to her or to mutual friends.
No pressuring her, and no asking her to compare you.
Whatever she decides, including neither of you, nobody holds it against her or against each other.
If one of you starts dating her, the other gets a bit of space without it being treated as a grudge.

This keeps things fair, and it can be uncomfortable for all three people. She may feel watched, and it can hurt more if you lose in front of him. It tends to go better when the group is easygoing and the stakes are lower, such as early interest rather than a long crush.

Option 3: He goes first, you wait

You agree he'll ask her out first, and you'll see how it goes. It's tidy. The cost: you're deciding to sit on a feeling for an unknown length of time, and if it works out for him, you may be around the two of them a lot. Set a limit for yourself on how long you'll wait.

Option 4: Tell her, and let her choose

If both of you are interested and you've talked, you can each let her know you like her, without pressure. Then she can say yes, no, or neither. This puts the decision where it belongs, but only works if you've both agreed to it first and can handle whichever way it goes. Don't make her choose between two friends in front of others.

What not to do

Don't go behind his back. Asking her out quietly and hoping he won't find out can come out, and then the secrecy may become a bigger problem than the original crush.
Don't recruit her friends to push for you.
Don't run him down to her, even in small ways.
Don't blame him, or yourself, for a "no" from her. If she says no to you, stop. Seeing her again after a no covers the next time you meet.
Don't make her feel like she's the thing breaking up the group.

If you've been seeing her and your friend only now admitted he likes her, you don't owe him an exit. Tell him plainly where things stand. Hiding it tends to cost more than the awkwardness does.

Staying friends either way

Whatever happens, a few habits protect the friendship:

Give each other a little room if one of you got what the other wanted. A few weeks without constant hangouts isn't a break-up.
If it ends with him and her together, be warm to them both. Don't ask for updates and don't talk about her to him as if you're keeping score.
If it ends with her choosing you, don't gloat, and don't make him a spectator. Check in with him on your own.
If she picks neither, you now have a shared story and a friend who knows how you felt.
Meet other people. Having options outside the group makes the whole situation lower-stakes. Social circle vs cold approach covers the tradeoffs of dating inside a shared group.

If she's a friend of yours too, how to tell a friend you like her covers saying it to her directly. And if the outcome is a no for you, getting over rejection without crashing out is for the rough days after.

What to do next

Write down what you actually know about her feelings, as opposed to what you hope. Be honest about how thin it might be.
Decide which of the four options above you could live with, before you talk to your friend.
Pick a private moment this week, and tell him in person using one of the lines above. Keep it under two minutes.
Agree on two or three ground rules, such as no talking each other down and no pressuring her.
Set a time limit for yourself if you step back or wait: for example, check in with yourself after a month about whether you still feel the same.
If she says no to either of you, accept it that day and, if you and the friend are both up for it, do something together soon.
Meet at least two new people in the next two weeks, outside your usual group.