Yes, it can be difficult. I think you have to consider two things before broaching the subject: (1) the basic attitude the person is likely to have about enemas and (2) the state of your relationship with him or her.
It was in the mid-90s the first time I worked up the courage to bring up to a girlfriend at the time the idea of adding enemas to our sexual repertoire. For some reason I trusted her in that regard, and I knew her well enough to have an idea that she may not be repulsed. For unrelated reasons, I was also not really enjoying our relationship by that point and figured it was something of a no-lose proposition. As it turned out, she was open to giving it a try, and I was able to finally share my fetish for the first time. In that case, adding enemas to the equation actually extended our relationship - probably too long.
Later, there was another young lady I dated seriously, and I was quite sure from discussions and our sexual play that she would be entirely repulsed by the idea. In fact, I strongly suspected that my bringing up enemas may very well be the final conversation we ever had. I realized that either we were not going to be sexually compatible or I was not secure in our relationship or, probably, both. It ended very shortly thereafter.
With my (now) wife it was very difficult. She was fairly open to experimenting sexually, but she had hangups when it came to all things anal. Ultimately I had enough faith in her and our relationship that I worked up the courage to bring up my sexual interest in enemas. She was not, and still is not, interested herself, but she indulges me by giving me an enema during sex play once per month or so. She also has no issue with me taking solo enemas as I wish. She even tried taking one a couple of times (which, unfortunately only confirmed her suspected distaste for them).