imo, rolentos worst matchups are blanka and morrigan.
blanka is madd annoying to fight against. like the poster above me said, its hard to standing mp on reaction to blankas jumps cuz its too fast. instead use rc scouter jump lp. my advice is try to runaway smartly and build your meter. try not to roll back or wall jump too much since random blanka balls hurts. dont fight him head on in the ground because his c.lk beats almost everything you throw out at him. make your way in with rolentos jumping mp and work on that guard meter. dont ever let him get in your face, because his crossup mk and low jump roundhouse are hard as hell to escape. AC your way out of there or if you are using A groove, blow thru it. last but not least, jumping mp works well against his electricity, hes a fat ass so its easier to cross him up, but the same goes for rolento, and its really easy to punish any whiffed c. fierces from him.
her jumping hp > everything you do in the air, its hard as hell for rolento to stop her crossups, and she can make your CCs whiff by flying above it and/or empty triangle jump. stay the hell out of the corner, keep her from getting in with the knives and be wary of her sweep. standing mk works pretty well against her. fortunately, almost no one uses her.
other sorta troublesome matches:
bison: standing mp beats every jump in bison does, just dont get baited by his jump in CCs.
ken: ambiguous crossup, fast ass dp and air hurricane kicks can kill you in a hurry. play rolento like you would play vega vs ken. fortunately its much easier to put a big dent if ken tries anything stupid like a random dp attempt.
chun li: fuckin annoying fight because its hard as hell to stop her from j.lk and j.mk without trading with standing mp. and those 2 moves along with j.hp shuts down almost everything you do in the air. her walk speed is faster than yours and she has some fast ass jabs. jumping neutral hk is also annoying. the good thing is that you can see her jumps a mile away so even if you cant punish it cleanly, you can evade it and rolento is damn good at that. and if chun cant get in, she cant land her super and if she cant land her super, shes not doing much damage.
this match is a lot like vs blanka, except much easier. like blanka, his jump ins are hard to stop. also like blanka its hard to attack him head on without getting counter poked. however vega doesnt do much damage unlike blanka and its easier to run from him since he doesnt have an instant torpedo attack. walk up lps works wonders against him since its hard for him to punish and it can knock his mask and claw off quick. once you get in, stay on him like white on rice. dont be afraid of a few hits from vega since the risk reward ratio is almost always in your favor.
cammy: imo, this is the easiest fight out of the above. the sweet spot is a few steps outside of cammys hk range so about half screen away. if she runs in, she risk getting swept or eating a knife. if she cannon drills in, and gets whiffed or blocked, free sweep or c.mk xx pipe spin. keep your distance against her by backdashing, back rolling, wall jumping, and/or rc scouter jumping. she got nothing against you in the air and theres almost nothing she can do to you from full screen so keep running. last but not least, shes one of the easiest characters to CC against since the majority of her main moves are grounded and all of her air moves are easy to trip guard CC