Presumably at some point you've had conversations with your partner about this stuff over the years?
So, I've been with DP for 20 years. The first 10 or so times we kissed, I asked if it was OK to kiss her. She always answered in the affirmative, so I pretty much knew that she was happy for me to kiss her. So I stopped asking. But I'm still looking for consent whenever I kiss her. I'll lean in, and wait a couple of hundreths of a second, to check she's OK with it. Sometimes I don't get it. Maybe we had an argument recently, and she's not quite over it, maybe she's just touched out from all day with a toddler, maybe she just thinks she's got garlic breath so doesn't want to. She stiffens, or doesn't lean in towards me. If I get any sign at all that she might not want a kiss, I check verbally. Sometimes I get it wrong, she's into it but I've read the sign wrong. Great, I'd rather have consent and not know it than not have consent and get it wrong.
DP loves having her back stroked. That's a 100% of the time thing. I don't ask. If my hand heads down to her bum and she's not in the mood, she'll tell me. We discussed that decades ago, it's settled. If she starts grinding her hips a little involuntarily, then I know I'm OK to put my hand inside her underwear. If I don't get that signal, then I'm asking first. It doesn't need to be "Please may I use my hands on your genitals", just a tug on the waistband and a "Shall I?"
And so on and so forth, a seconds wait before entering her, or her knowing that I'm only ever happy to have a blowjob if I've showered before bed. A finger or more up the bum is always ALWAYs a verbal check, because I know that she's sometimes into it and sometimes not, and I have no non-verbal cue to what shes feeling that night.
What you can assume and what you need to check in every situation is something you learn with a partner over weeks, months, years, and even decades. You start off asking about everything and then you slowly learn what the non-verbal cues mean. And if ever something feels off, or stiff, or quieter than usual, or just wrong for some reason, you stop. Instantly. And you talk about it and find out what, if anything is wrong.
OP was with a newish partner, and he did something that they'd never together before. And he didn't ask, he didn't check. He had no way of knowing the non-verbal cues, because they'd never done this before. He couldn't have known whether he had consent. As I said before, silence is not consent. Freezing is not consent. Him guessing "She's OK with this" is not consent. Therefore he did not know if he had consent. Sex without consent is rape. He is a rapist.