I have a richer, more balanced sex life since becoming poly. There doesn't seem to be any fear of comparison between my partners, and I also don't do that. I notice differences, obviously, but a ranking doesn't follow from those. I enjoy various things genuinely.
For me NRE with one of my partners had the most effect in that relationship, but it also had an overall effect of a higher sex drive. Now I'm not in NRE anymore. However, I am in a long-distance relationship with my girlfriend Mya, and I have noticed that I have more sexual energy when I have both of my partners here with me. I don't know if it has to do with simply being jazzed about seeing her and thus feeling more energy in general, or with a feeling of balance.
I do think there are some things that are challenging in terms of sexual energy, but I haven't found any that are poly-related. I tend to have low energy overall at times, but that is no different from what it was before.
I think poly/nonmonogamy can be good options for couples who have different interests or desire levels. From what I have seen, I would say that poly/nonmonogamy are less likely to work as a solution to a problem if solving it is the only motivation to become open and the people in question would otherwise never consider it. However, many people do seem to find very much satisfaction in openness when they decide to do it, and differing interest/libidos with one partner can become less significant to overall sexual satisfaction.
I certainly feel that my sex life has become a lot more satisfying since becoming poly, because the dynamics I have with both of my partners are very different. I was craving for some forms of sexual expression before, and I did explore things with Alec, who was my only regular sexual partner at the time, but even as he wasn't against it, they just didn't feel natural in our dynamic. E.g., I am a switch, but with Alec I have very strong urges to submission only. Some of the things are also the kind that he simply can't provide, such as being with a woman. I feel a lot more satisfied and balanced with being able to express multiple facets of my sexuality. I also feel more comfortable with my sexuality when I have balance.
I haven't encountered pitfalls in having different sex lives with different people, only benefits. And same is true for my partners sex lives with other people as far as I have experienced it. I don't have any specific boundaries. I am not freaked out about STDs or pregnancies at all, because I use effective birth control, play safe, and have no reason not to trust my partners to do the same.
Here is something I have written about sex earlier, I thought I would share it here
Originally Posted by rory
My sexuality has been through changes, and probably keeps on changing. At times I've felt like there is too little common ground for me and Alec to be able to make it work. But (in addition to having done lots of work and thinking and communication) there have been lots of positive effects poly has brought to my sex-life as a whole. There are such differences in gender-dynamics, but also in power-dynamics, in my sexual relations with both of my partners, and that has made a huge difference. I feel more balanced when I can express different sides of myself. And I have gotten some needs (or strong wants) met, of which some I likely couldn't have identified very clearly. But others I had identified and concluded not easy to meet when in relationship with Alec: most obvious one being having a woman as a regular sex partner. Before meeting Mya I didn't consider poly-relationship as a real possibility, and even in an open relationship possibilities for sexual encounters with women didn't come up very often (likely since I only feel attraction after I form a connection with somebody, so don't have sex with strangers); certainly not comparable to having a relationship with a woman. The gender-thing is not the only one, but my point is that I am overall more satisfied. And I feel that I can enjoy the dynamic that comes naturally for me and Alec when I also have a relationship with a different kind of dynamic. That is, I don't need to try fit all aspects of my sexuality into sex with Alec if he is no longer my only regular sex partner.