I speak to a lot of people in a lot of different contexts about sexual consent. I always advocate for asking before you engage someone in any kind of physical contact. A lot of people tell me that they don't like to ask directly, especially when it comes to kissing or sex. It spoils the mood, they tell me. And it's awkward.
Here's the thing, though. If you do value/want consent (which I hope you do!), and you don't ask your partner directly if what you are doing is OK with them, then the primary way you know whether you have their consent is by their body language. But body language is notoriously unclear.
For example, take a look at the picture below. Do you think the woman in this picture is enjoying the kiss she's getting? I can see that she might be because she is smiling, and she's standing pretty close to the guy. But on the other hand, she isn't looking at him, and her head is kind of tilted away, and her hand is lodged between them. Honestly, I could convince myself either way on this one. But he has clearly gone ahead and made his move. I sure hope he asked first, or it seems to me that this woman might be receiving a kiss she doesn't want.
And that's my main point: if you are relying on body language, then you're taking a much bigger risk. Your partner may not actually be into your advances and you risk hurting them. The risk is much less if you had asked for consent, and you will have confidence that you are not causing any pain. And, let me tell you, someone who is involved in a kiss (or something bigger) that they don't want feels a lot more negative feelings than that slight awkwardness you were trying to avoid by not asking. When someone is overwhelmed by these negative feelings, they are definitely not experiencing the mood that you were trying to avoid spoiling in the first place.
So go ahead and ask! The worst that could happen is they say no. And if they do, then you've successfully avoided making them feel pretty bad about you.