Being friendly to a family member is totally normal. Women should not have to wear sackcloth and ashes and avert our eyes to prevent tempting the menfolk you know. This man has basically told her he's entitled to her affections, put her in a terrible position viz. her husband, made her feel vulnerable and afraid. Not ok, just not ok.
I'm reminded of something golda Meier once said - there'd been a spate of rapes in Israel and conservatives were calling for a curfew for women 'to keep them safe.' She pointed out that it was the men who needed the curfew - it wasn't the women at fault.
This will come back and bite you if you're not open with your dh. But phrase it well.
" sit down, the weirdest thing happened today. I want to talk to you about it because it's made me a bit angry and a very unhappy. Uncle came by today and told me he loved me, can you imagine that!? I was just floored. I'm so annoyed that he put me in this position, he had no right to do that, I don't know what he's thinking. He says he "doesn't expect anything but wants to give me time to think."
That made me really annoyed, because he's just dumped this on me - now I've had to have this conversation with you, and now we have to think about how best to handle this together. Poor aunt! I need you to not get angry at him (note him, not you, you DO NOT APOLOGISE for any of this, don't let it be turned back on you) but I need your support here, and I need you to be calm and support me."
If he starts any kind of " what did you say to lead him on" shit you need to cut him off very quickly and say something like
"I'm sad you'd think that. He's a family member, im as friendly to him as any other family member. He had no right to do this to me. This comes from him, not me. I'm angry and upset about it, as I have every right to be. I can see why women get so upset at things like cat calling etc, you're just minding your own business and some guy thinks he's entitled to your body. That's not ok, is it?"
Good luck op. Awful situation but absolutely not your fault.