Does it die/melt/decompose in the heat?
No ... the viral lipid bi-layer does not "melt" at room temps and seasonal fluctuations in "incidence" (how many are newly getting the disease) have nothing to do with ambient room temp ... CoVID-19 is far more stable than this rumor suggests ... what you're talking about is pasteurization (where proteins are denatured and lipid micelles ("bi-layer envelope") degrade - not melt) and that happens north of 140 ... CoVID-19 remains infectious about 3 days on cardboard, 9+ days on solid surfaces and about 3+ hrs aerosolized
What is interesting is that it seems that other Cononavirus seem to lose their infective potential (R0) in warmer months ... current thinking is that may have something to do with warmth and/or humidity impacting the method the virus uses to insert itself and hijack cellular machinery ... jury is out on this one right now
Flu susceptibility increases in winter, increasing the reservoir of infected ("prevalence") ... susceptibility decreases in warmer months, decreasing prevalence ... the low R0 for INFLUENZA results in the infection dying out as a result ... temp does not meaningfully affect the virus itself ... CoVID-19 has a higher R0 than Influenza meaning that roughly double the infections will result from each infected ... that is a recipe for increasing infections until we can break the transmission cycle The other two major other coronaviruses (MERS, SARS) "died out" in warmer months only because we figured out how to trace exposure and quarantine those exposed *COINCIDENTALLY* in the summers ... Its unclear if the decreasing incidence had anything to do with "warmer temps" driving down infections ... studies are looking into that now