How do you show her?
1- Tell her quietly and calmly that if she wants you to leave, you will go. "XXX, it's pretty apparent that you are unhappy and I'm sorry if I'm partly responsible for that. If you want me to leave, I will go. No scene, no discussions of the past, no tearful goodbyes. All you have to do is say the word".
2- If she says 'yes, leave', then go, right then. Don't say "OK, I'll be gone as soon as I make plans". As misssmith says above, have a plan. So don't initiate this conversation until you have a place to go, even if it's to a hotel.
2- If she says she 'doesn't know' or 'isn't sure', tell her that saying that gives you hope where perhaps there is none. That she needs to let you know if there is hope because you would like to save the marriage.
3- If she says there is hope, tell her that you will be going to an AA meeting on XXX date (like tonight or tomorrow) and that you will call your GP for counseling referrals tomorrow morning.
4- If she says there is no hope or refuses to give you a straight answer, what she has been saying may be because SHE has already made plans to leave but wherever it is she is going isn't ready or available right now or she's setting money aside. You can ask her if she is planning on leaving herself (assumably with the children) because you need to be able to make your own plans, but she doesn't have to tell you.