Why is my cat acting this way?

So originally we had 3 animals in our house, a dog and 2 cats. Recently withint the past month we had to put our dog down because she had cancer and it had spread, and the night before one of our cats suddenly dropped dead of an unknown cause. So that now leaves us with one cat in our household that has latley been acting strange/ out of the ordinary and wonder if anyone can shed some light on the subject? Before both our other animals passed this cat stayed only around me and wouldnt come out around anyone else and was basically a frady cat 24/7. Our other cat *the one that died* was a huge attention hog, and our dog also loved to get alot of attention.anyway Now hes outgoing and constantly keeps meowing and we have no idea why he is. Were thinking perhaps he is lonley or misses his companionship of the other animals in the house, and we have been cotmplating getting a 2nd cat like a playmate for him? i know from reading cats usually tend to like being alone or can be alone for a while before needing compaionship, which hes usually alone about 4-5 hours a day before someone gets home. Why is he acting the way he is? is it lonleyness? or is he content? and should we consider a playmate for him or leave him as an only animal?