This isn't about throwing out her computer or telling her she can't contact the other man in your house or any number of a thousand things while you are in the house together..or having a temper tantrum about how you aren't going to be walked on. (while she walks on you in your own house despite your tough words) That is like telling your child they can't do drugs in front of you, so go in your room and do them. Just don't do it in front of me.. That is silly.IF you are going to do drugs it isn't going to be in THIS house. Find somewhere else to live.
If you want to show REAL tough love and show her how serious you are THEN you tell her that YOU HAVE DECIDED that you are no longer going to live this way and you have decided you want HER to find another place. ASAP. Since she wants to have OM in her life then YOU have decided you will NOT live that way. So, tell her that she has one week to find a place of her own and she can then be FREE to do whatever she wants with whomever she wants..
THAT is what tough love is. If in doubt then read the original author of tough love. James Dobson. APPEASEMENT does not work. Telling her she can't contact the OM in front of you or anything like that is still WEAK. Get tough. NO MORE. If you choose to contact him, then you WILL do it from a place you live in without me...