First of all, no not all immunocompromised people develop warts. That is completely wrong.
Some people develop warts and some people don't, its just what it is.
You may have been carrying it for sometime now, it is definitely possible that your hpv was latent and dormant but decided to pop up now. Your ex may have been infected with another strain as well that causes warts but like you she never developed warts since most people tend to be asymptotic.
I would not worry who i got the warts from, the thing you should do now is treat the warts. Aldara helps the immune system recognize the infection so that it may fight it, also it may take up to 16 weeks of use for the medication to work. Usually Aldara works better in women than men, not sure why.
Getting infected via towel or secondary items is not possible. (says Dr. Handsfield)
You should consider getting your fiancé the Gardasil vaccine if she has not, not sure how effective it will be but definitely something to consider.
HPV is not a life long chronic infection, most people usually clear the virus within 8-24 months, thats just the average. Just treat your warts and sooner or later they will just have been a minor inconvenience .
Im sure your sister and mother don't have any problems from HPV anymore since they have most likely cleared it, right?