How to deseed a guava?
The only ways I've figured to use the inter-seed pulp is to juice it or mechanically sieve it, such as in a food mill, coarse stainer, or colander. 

This article from EHow suggests to blend or process the seed-pulp mixture, possibly with a bit of water, then sieve or strain. It might be possible to blend slowly enough to disrupt the seeds without pulverizing them. It sounds like guava seeds are edible, so if you damage them it's not harmful, but may make straining more tedious or less effective. I use a manual food mill and it works adequately.

If you're going the pure juicing route, see also this previous SA question on how to make guava juice. 

I have the same problem with other fruits with similarly tricky seeds, like prickly pear cactus fruit. Pages like this one a rather brute-force (or perhaps "scorched earth") sounding policy of juicing the whole thing. 

However, all of those are a little dissatisfying (to me) because they destroy the texture of the flesh, and oxidise even more quickly.