Sims sometimes don't get jealous if they are occupied or you have a few tasks lined up. I just try harder not to get caught on those types of sims. I personally liked it better when it was less there but I understand the tweak if this was done.
If you consider a sims life span 3 days is quite awhile. I don't try to cheer them up except for work and then they get sad at work when whatever I did wears off. I guess when they feel the need to be social it's easier to get angry for some of them I don't know I have them paint and sleep and clean ect mostly. I think the anger is also more prominent for other traits since their happy interactions are pretty severely limited when they are sad. I kind of think they have tweaked it some my sims are sad for about 3 days for this and death and it's more often than it use to be for me. So your statement about them not caring isnt true it took me three full days of making her use friendly interactions with him until he stopped feeling sad and stopped brushing her off when she tried to talk to him he got angry with her then went to bed and sobbed his heart out (made me feel awful that id done that to him).
I deliberately made my sims wife cheat on him (this was ages ago when TS4 was first released) to see what reaction id get from the husband. If the relationship bar and romance bars are high enough then the partner that was cheated on will get angry and/or sad. Don't worry, your sims won't give a flying fig if their partner flirts with another. The sims are so advanced that they are naturally able to block out everything that goes on around them, including cheating. The sims 4 has made that reward obsolete.