As tough as it may be, and however nice they seem, you should never lose sight of what they are and why they are doing it. They want to make money.
I recall a secondary school joke where a girl points to her crotch and says "with one of these, I can always get one of those", pointing to the guys dick area. It's crude but true, and we should never forget.
In my early punting days, I was smitten by a slim blonde 20-something from Sheffield, very willing, slightly sub, stayed over time, and saw her more regularly that I should have, which made matters worse. Thoughts of her kept me awake at night. Daft, innit? I almost felt like a protective father figure, given age differences, so there was another set of emotions coming into play.
Nowdays, I dont have any emotional attachment to a WG, just find em, fuck em and generally forget em - with a couple of exceptions where repeat visits are warranted because they are damn good, but not on a regular basis.
Thing is that she's doing this 3hs for £180 to you, are there others? She only needs a couple more seeing her frequently, and that's a nice tax free income too.
It'll be hard to move on, but do so you must - and you will feel better for it too. Then gradually, the emotional attachment will diminish.