Interesting question. I don't think I've ever "fallen in love" with anyone in the lifestyle.
I do however, believe that deeper feelings do develop if you meet with someone and are intimate with them on a regular basis. We have a "friend" that we have known now for probably 8 years or so and get together with him on a regular basis. I don't think I'm in love with him. But I think I have strong feelings for him because we have shared intimate moments, spent a lot of time together and had a lot of fun. We talk a lot. We hang out a lot, and spend a lot of time together. Throw in the fact that we are sexual together, and yeah, I'm pretty close to him. Close enough that if he moved away or if we stopped seeing each other, it would be disappointing because we are pretty close. (By the way, he and my husband are very good friends too.)
I would also point out that I am madly in love with my husband. We are best friends and have a very strong and open relationship. He knows what I like, what I don't like, and our marriage is really good. (Don't take that as perfect--sometimes I want to put my foot so far up his ass... lol) I'm very lucky. If my husband said we needed to stop being in the lifestyle (which I don't ever see him doing) but if he did, I would do that in a heartbeat. No questions asked. Some disappointment for sure. But no questions asked.
Just my $0.02