Few notes:
"You will get better by finding players of equal skill." No, you won't. You only get better by getting rekt and understanding why you got rekt. You don't get this through playing casual players. Casual players aren't showing you spacing or teaching you when to tech or which way to block. They're jumping around like a scrub like you.
"How many hours do I have to put in to get better?" At least 30 a week. There's a Jwong Q&A video somewhere where he talks about how after school he'd play the cpu on MvC for 3 hours a day and how he'd be at Ctown Fair every Saturday at 10am waiting for people. Nowadays you can do this in the comfort of your own home.
"I learned all the combos and still get rekt" So speaking strictly from the most popular game, SF right now, combos are not what make this game. You have to understand what frames are. You have to understand what footsies are. You have to understand what crossups are. You have to understand frame traps, overheads, teching, fast/slow wakeup, links, feints, etc. You really need to dedicate time to reading, watching videos, watching streams, and playing playing playing playing.
Look up JWong playing MKX, or better yet go back to last week or launch week and watch him play people online. He bodies everyone with one simple technique - crossups. 99% of stream and tournament monsters have no idea how to block crossups and they lose 25% of their life every combo. It's so sad to watch. Op mentioned how he doesn't know how to guess high/lows or crossups. There is no guessing. A good player can see/read it and react accordingly. A great game to see this in is SFxT where one normal can lead into a 30% combo. Watch old streams and see how easily people can read the overheads. Or watch videos of Sako (like the recent Daigo fight at Topanga) and watch how Daigo knows how to block every mixup setup.