Now that’s a good question. If it’s temporary, abstinence would seem to be the best answer, no?
A chronic condition would be more difficult to define. I posted a very similar question a while ago to see what answers would pop up about condom use destroying the unitive aspect of intercourse (assuming that we are talking about a married couple).
My hypothetical involved a woman who would get, say, vaginitis without a condom; not life-threatening, but would require medical intervention to get under control…something more than a mild, self-limiting vaginitis.
I admit that this is a teaching that I struggle with a bit. The best answer seemed to come down to that the unitive aspect is destroyed by having a physical barrier between the two partners. What I struggle with is that there would also seem to be a loss of the unitive aspect of marital intercourse if the couple had to practice constant abstinence due to such a condition.
My struggle is to try to reconcile the Church teaching on the unitive aspect of marital intercourse without falling into the trap of relativism, i.e. which unitive aspect is the lesser of two evils to lose, the total loss of intercourse, or the loss of the unitive aspect that occurs with condom use.