Preface - my comic is a mixed bag of a lot of things, but Grassblades ultimately tells the story of one man's recovery from severe trauma, so there is a lot of darkness in there. It's not dark ALL the time (I take time out to tell super-dry dad jokes and draw adorable little girls picking flowers, etc.), but there's an undercurrent.
Suffering, as with all things in a story, needs a purpose. Suffering in and of itself does not a good story make.
It's perfectly possible to tell an entire story super-well without the character ever suffering. There's a difference between suffering and overcoming obstacles. The point is to give the character something that hinders their progress, something they need to work around or work out how to overcome, not to cripple them just for the sake of putting some suffering in there.
To use my own main character, Masahiro, in the most non-spoilery way possible. He's lost his left hand from the wrist down - which used to be his dominant one, meaning he now gets by using his non-dominant right hand for all things. There's also a pretty nasty magical infection thing going on, which leaves him with one heck of an uncontrollable magical anger problem. A lot of his character arc is centered on dealing with these issues - how he tries to get around them, how he fails, how the problems get worse over time, how he desperately searches for some way to cure himself, etc.,etc. - but while they're the center of his character arc, they're not the entirety of it.
The suffering is motivation and complication, but it is not the end-point. He's not suffering for the sake of suffering - he's suffering because it's giving him reason to get up and go somewhere in the story.
Look at it like this - if you suddenly pull the rug out from under your character right as they're poised to succeed, it doesn't always make them more relatable; sometimes, it just frustrates your reader. Make sure you do it with purpose and then build on it - piling failure after failure, or suffering after suffering, on a character, without letting them have moments of triumph every now and then makes for a pretty predictable and boring story, IMHO.