Sigh.... Okay, the initial shock I can understand, it's a weird thing to walk in on, but for the love of radioactive spiders, GROW A FREAKING PAIR Parker!
This is the woman who raised you, and has been a widow for many years, she meets someone she cares enough to want to sleep with. I'd say she's pretty much got that right, and the least you can sodding do is support her.
It's the sulky "I can't handle this right now. I have a lot going on" crap which seals it for me. It's not about you Peter, not one single, solitary, isolated bit of it, so be a decent human being and wish your aunt well. Otherwise expect Uncle Ben to rise from his grave and bitchslap you for denying her a chance at happiness.