Background: Got SF4 about a month and a half ago. I've been playing online alot lately. I play Rufus since i like his style and i'm most familiar with his moves.
 
The situation: I don't get it... I lose but I can see my opponent doing everything and i see myself doing stupid things like jumping into a fireball or accidental ultra/snake strike. I understand the game mechanics now, is it just more practice? Should I be spending more time in arcade mode? Should I learn more characters? Watch matches online? Get a fightstick? Keep playing online? iduno anymore. Maybe I'm taking the loses too seriously? 
 
lay it on me! i can take it >.>

Street Fighter IV is a slightly more complicated game of rock, paper, scissors. The game is based around spacial zoning of the screen and effectively using your opponents strength as a weakness. This could come as, you baiting a Shoryuken from a Ken player, waiting for a Headstomp by M. Bison so you can throw him mid air or getting a Ryu player into a pattern of Hadoukens so you can jump over one and attack him while he is still recovering. This is using a players srength against them - you take the strength of a projectile and immediately turn it into an opening for an attack.
 
However, there are some moves, which when a counter move is thrown, only one of two of the moves will hit, and this is where the rock, paper, scissors metaphor makes a bit more sense. If you cross up a Ryu player with a FK and then low jab him three times, unless you then follow that third jab with a special move, if he throws a Shoryuken, that Shoryuken will ALWAYS take priority over your jabs. This is why spacial zoning and baiting are such a huge part of the Street Fighter tactics.
 
I had the intention to say less specific things and more general ideas, but it didn't work that way, haha.
 
I think before you can truly get "good" at the game, you need to, at the most basic level, understand the fundamentals of the combat and how everything works. When you do this, you can truly understand the game as a whole.

Its a steep learning curve .

Practice and seek knowledge, simplest answers that reap the most reward.

If you got a friend locally invite him or her over one night . Play some local and see what characters you like and have some fun  . Thats what i did . Online is laggy as hell on street fighter 4 so playing locally is much better . I bet you won't loose so much if you play offline .

Find a buddy to play with, even if they're even worse than you.  Just having another human willing to help you out will make you better.

Other than that, learn the ins and outs of the game itself, learn a character, and seek out tips and strategies from Youtube, Eventhubs.com, the forum here, etc.

It'll click eventually.

Go to http://mycheats.1up.com/view/superguide/3163881/street_fighter_4/xbox_360 and read their character guides, watch the combo video if they have it. Then go on youtube or http://streetfighterdojo.com/index.html and watch some match videos to see what you read in action. Then go online and try some of it. Don't worry too hard about link combos and execution right now, just work on basics like anti-airing, teching throws, and punishing. It'll still take a while but eventually you will get good.

I'd say most likely you are just too predictable and it seems like you are doing stupid shit because your opponents have baited you into doing what they wanted you to do. When it comes to mind games the cure is play some more.

more, i believe, if you count some of the really bullshit ways you can land his ultra or the extended combos.  Lets seeeee:
 
Messiah FADC,  jumping double roundhouse, Target combo, -> Fierce (into SS first if you like), HP tornado in the corners or 1/4 of the cast at mid screen (do this on rog in training, it looks freakin hilarious).  The tornadoes are the scariest considering he can dive kick into safe tornado pressure and you're just sitting there hoping not to bounce off a corner after you eat one of them.  im sure i missed a few, but yes, learn rufus's crazy ultra game, it helps a lot.  :D