If she has a good job offer, then she will shortly have the ability to pay for her own place to live, if she doesn't have that already.

If she has a short term liquidity problem, an option would be to lend her some money if she does not have access to short term borrowing from a credit card. I personally would not do that either, but lending her some money would be far, far less intrusive than taking her in.

I find this to be really quite unreasonable. But the fact is that it will be very difficult to kick her out, no matter what the stated, "definite" timeline might be, if she is not ready to leave.

And it should not take 3-5 months to find a new place.

Personally I would not see this plan as a favor so much as an imposition. People who move to new cities to accept good job find their own places to live. That comes with the territory. She can ask her new employer for help with finding a new place. That would be much more reasonable in my view.

Aside from all of the above, it took so much effort and time to get to live with him, and you two have had your hearts set on this for so long, that it pains me to think of you having any roommate, much less a co-worker, being present in your intimacy.