Frustration with army splitting

A long and frustrating night on the ladder. Looks like I went 5-16! I lost to all varieties of cheese: zealot rush, ling rush, cannon rush. Twice I played the same guy twice in a row. Once was a 4-gating protoss who I lost the first to due to a bad supply block but beat handily the next game with 3-gate into blink. The other time was a drop-happy terran. I beat him the first game with good map awareness to shut down his drops but then lost the second even though he did the exact same thing and I was ready for it, shutting down his first few drops and getting a big supply lead. Eventually he just wore away at me with endless dropping and forced me into bad confrontations.

The most memorable loss was a PvZ though. I started my 3gate but scouted an early 10-pool and stayed defensive. It was a big roach/ling rush at about the 5min mark. I held it off and expanded, trying hard to set up walls connecting my expansion. My scouting revealed a huge pack of speedlings roaming around so I stayed tight to my base. The game turned into collosi vs burrowed infestors, followed by brood lords on 4 and 5 bases each. He wore me away with better eco. But afterwards he messaged me and informed me that I had the game earlier if I just attacked. Watching the reply I held an enormous worker lead after the roach push: 32 to 14! But the speedlings kept me locked in my base and I never felt safe to move out, just letting him drone hard to catch up. I should have put down a cannon or two and left a few zealots guard and kept pushing.

I was raging a little bit by the end, having stayed up later than I should have and getting tired. I don't feel like I learned much. I just ran up against my diamond-level demons, losing to the things I know I lose to: cheese, multi-pronged attacks or threats of multi-pronged attacks (i.e. speedlings). Some of the games I lost to mistakes that I shouldn't be making. Those games I get much less frustrated with actually because I know what to improve and know that I can. The ones that frustrate me I feel like I have no idea what I can do to improve. Because I come out of them needing to do the same things I've been needing to do since day 1 and just can't seem to: split up my army and micro.

I felt terrible when I logged off but the now the next day, I'm not as hard on myself. I only barely failed to hold some of the cheese attacks and knew what to do but just executed a little late or sloppily. I can fix that. Some games I lost to build orders that I just have no answer for right now (one-base collosi all-in and one-base polt all-in) and I think I need to expect that in some cases till I refine my own builds.

So I'm left with the army-splitting problem primarily. How do I train myself to do that?