Im headed off for the night after a way too long workday. Short response and ill follow up tomorrow when i get some time. Its natural for feelings to develop. It usually means you're at least doing something right thats making the other side so happy with you and so comfortable with you. I have this happen lots times and its honestly part of it. A dynamic is a very connected deep thing and once those walls of hesitation are down and the trust builds i think feelings just naturally happen. I mean dynamics are in all actuality, relationships. Thats why many people suggest seeking out doms or subs to be like seeking out a bf/gf.
A few questions to help better answer further.
1. Did you develop feelings for them as well?
2. What reasons did they give for having feelings for you?
3. Do you have a perm vanilla or other type relationship thats providing the love affection portion of your life?
4. You say long term slaves but long is subjective how many months, or years are we talking each one lasted?
Simplest answer is, if youre not happy with this type of result make it clear upfront youre not in it for that... it may drastically reduce your options but at least you wont end up there a 4th time. Also you can just treat it as more a top/bottom situation as casual play partners if thats more what you want. Again this might reduce your choices. Some people are better at compartmentalizing than others so every case will be different. Id suggest asking yourself with the last few that felll for you, if they had said they were in love with another but wanted to still sub to you, how would that make you feel? If the answer is youd be bothered by them wanting to love another while playing with you then maybe you had some feelings too. Ive had both ways and all relationships have progressed differently. Some even ended up with feelings when neither was seeking them out . Its a deep connection things happen.