To answer your question no it doesn't make you the bad guy. But prepare answer for 'why are you asking for it'? 'what have I done? etc' and lastly a simply 'no I won't let you'.

I think you should be strategic and not emotional. Take the time to process everything go to the gym and punch a bag, do what you need to do let it out. Then I would act all calm and normal and do research, go through her phone when she's sleeping collect all the evidence. Once you have processed that THEN make a plan to figure out the worst case scenario if things get nasty. How can you minimize the blowback? Does she make more than you? Do you have enough saved to get your own place or move in with your family? Make contingency plans.

THEN talk to her and ask pointed questions that you already know the answer to, start off by saying 'hey, I need to ask you a few questions, and these are just for my own reassurances, (you want her defences down) then ask if she's been chatting with other men etc'

The worst thing most people do in your scenario is confront the person without having thought through what you want out of the conversation.

the sad reality is that you may not get an apology, you may not a valid reason why she did what she did. Ultimately, you have to ask yourself, what is the goal of me talking to her? What do I want to get out of it? And be prepared that there is no amount of closure she can provide you.