Both Rin and, to a lesser extent, Jess have an extremely open and active sexual lifestyle during the band years - to the point of practicing exhibitionism during their shows and eventually inviting show-goers on stage with them to join in (which typically extends an open invitation to join them afterwards as well).  They are also both extremely heavy drug users - primarily marijuana, cocaine, and heroin (as opposed to, say LSD).  However, there are major differences between the two of them and how they go about these activities.
Rin does not exercise caution.  At all. In the slightest.  (With the exception of condoms sometimes as that is typical practice.  Even then, this is a rare occurrence - if someone does not want to use them, she will not force them to do so.)  She assumes that her partner is clean in the same way that she assumes that her needles are clean - which is to say, they might not be but she will often believe they are regardless.  This is less naivete and more simple recklessness.
Jess, on the other hand, after her first STD due to Rinâs assuming influence, is much more cautious.  She will always ask to make sure their on stage partners are healthy, and when they arenât, will refuse to participate in anything after the show (on stage is primarily for hand stuff - which is not to say you cannot contract things that way, but that unless she has a cut on her hand, it is much less likely).  Even though Rin will not make sure of a condom or a clean needle, Jess will.  As a result, even though she still gets STDs, they are significantly less common, and with two exceptions, she doesnât get pregnant.
Rin has probably gotten pregnant multiple times, but she views this like a disease and treats it accordingly with pills and abortions.  The first time Jess was pregnant, she did have an abortion but she told no one (primarily because it was Kyleâs child).  She is less likely to view pregnancy as a disease, even though she has an extreme fear of it (due to pregnancy being a major influence in her motherâs death).  The second time Jess planned on following through with the pregnancy - abortion being a traumatizing experience for her - but lost the child (it was stillborn).
That said, when Jess became pregnant, she cut everything out of her lifestyle.  No drugs, no sex, no nothing that would harm the child (with the exception of a glass of wine every now and again). She stopped everything cold turkey, and although she still drinks afterwards and may indulge in cigarettes or marijuana, she primarily remains clean.
On the other hand, while Jess was pregnant and Rin was preparing to be the childâs other mother, she did not quit her lifestyle and, in fact, contracted HIV from one of her sexual partners at the time.  Rin did not find out about this until much later, after her return to America - three years at the least, although it is potentially longer.  Rinâs recklessness led to a refusal to have herself tested until she had another STD for which she needed medication, which means she is just as likely to have spread the disease to other people as well under the belief - the assumption - that she did not have it.
The only reason Jess did not contract it from Rin is that during the time period Rin had it 1) Jess was not sexually active and 2) Rin was in Japan away from Jess.  By the time Rin returned to the states, Jess had moved on and was not interested in pursuing a relationship with her again.  However, if Rin had contracted HIV earlier, Jess likely would have gotten it from her - because regardless how many times Jess told Rin to get herself tested, and regardless how many times Rin told Jess she got tested, she never did unless she needed medication for something that already showed up.
I expect that Rin dies by the time she is 35Â due to her recklessness.