You don't give us any information about you aunt's status, like whether she's married or not? If she's a single woman, divorced, widowed, or never married. then really, there's no reason why you shouldn't have sex with her if that's what you want. It's fairly obvious what she wants. If she has gone without sex for a long time, it's hardly surprising if she sees you as an opportunity to enjoy herself with very little risk. Her predatory behaviour is all aimed at getting you into her bed, and I do sense a certain hesitancy on your part.However as we don't really know the full extent of the circumstances, it's hard to judge what is causing your reticence.
On the other hand, she has a husband somewhere around, then this is a dangerous game to get involved in. As I've said many times, other people's morals are not my business. However I do concern myself with the consequences of their actions, when they write in and ask for advice. If there is a husband around, then there will definitely be consequences if he catches you with her. So think very carefully about that before taking any precipitate action.
You obviously enjoy this lady's company tremendously, and she obviously feels the same way too, so sexual attraction is hardly surprising. If the two of you want to have a sexual relationship, no advice here will make any difference. But if you have doubts, don't let things escalate until you've determined how you feel. Don't get pressured into anything that you might regret later.