If they can't or won't engage with the conversation at all — they deflect, freeze, or get upset — that isn't a problem to solve by asking better. You can still keep your side of it: no pressure, no re-asking, no penalty. A conversation takes two willing people; your boundaries only take one.
This talk also doesn't have to happen in one sitting, at full length, or out loud. Shorter, split across moments, or written down are all legitimate formats — especially with a trauma history, difficulty putting feelings into words, sensory sensitivities, or simply a body having a bad week. Not following a script isn't failure; the pace belongs to both of you.
Some context on why this matters: in a diary study with young couples, about one in six reported sexual occasions they went along with without actually wanting — often to keep the relationship smooth. When someone doesn't feel free to refuse, agreement becomes compliance. Its consequences vary hugely from person to person — which is exactly why "they went along with it" tells you nothing about whether it was okay.
So if you catch yourself persuading — rephrasing, timing, guilting — stop, and read what pressure looks like (below). And if what's actually between you is a long-term difference in desire or frequency, not one preference, that's a different conversation — also below.