there is no real change in context. It's pretty much how 小さい 小さな and such that can go either way. Although, in the case of happier/more happy, Happier sounds more common and some people might correct you if you say more happy.
I know the Longman is better for ESL study, but merriam-webster.com is great too because it has audio samples of nearly every word.
Main Entry: hand·some
Inflected Form(s): hand·som·er; -est
Etymology: Middle English handsom easy to manipulate
1 chiefly dialect : APPROPRIATE, SUITABLE
2 : moderately large : SIZABLE <a painting that commanded a handsome price>
3 : marked by skill or cleverness : ADROIT
4 : marked by graciousness or generosity : LIBERAL <handsome contributions to charity>
5 : having a pleasing and usually impressive or dignified appearance
synonym see BEAUTIFUL
- hand·some·ly adverb
- hand·some·ness noun
I know the Longman uses international phonetic symbols to indicate pronunciation but I'm just showing this sample to show what you can focus on. In general, the bold part is what you will look for in your dictionary when trying to learn how a word is inflected. However, even English speakers reguarly make mistakes here. I didn't know Handsome inflected, I would have sworn it only could be used "more handsome". This is why when in doubt use "more" or "most"
In general, 1 syllable inflect if you know it. 2 syllables you should probably inflect if you know it, but you can also probably use more/most if you can't remember. 3 syllables or more, few people will notice if you use more/most.
Most adjectives you can learn as you go. But there are some irregular adjectives. good > better> best. bad>worse>worst. and so on. These you need to memorize. Because making a mistake with an irregular verb really calls attention to itself.
good better best
bad worse worst
much more most uncountable nouns
many more most countable nouns
little less least
little smaller smallest