“Isn’t there such a thing as if you do something 3 times, it’s a shvuah?”
That’s only a dvar mitzva, or something that there is a halachic reason to do. However, since your Rav has said that there is no inyun not to type, you not typing was not a dvar mitzvah, and therefore I would assume there was no shvuah. However, as aries2756 said, if you truly have a problem you should consult your Rav.
“If I told the secular ppl I work with that I try to not type on CHM, then got a psak from my Rav that I can, should I do it or not, should I bother to explain it or just let them assume I’m less strict than I used to be?”
I would imagine that if you don’t tell them anything they’ll assume you simply don’t keep that halacha anymore. Therefore, I would assume you should explain the situation to them (although I’m not sure how exactly how you would do that) to avoid a chillul Hashem. However, as always, all halacha li’maseh shailos should go to your LOR.
“Is it ok to type something if I know my secular coworker will probably print it out for themselves?”
Hmmm… that sounds suspiciously like a halacha li’maseh shailah, one of those things that should be asked to your LOR.