There are two things wrong with this question:
• If you have to ask, there's about a 90% chance you're doing something wrong.
• Cheating seems to be a pretty cut-and-dry concept: if you're having some form of sexual relationship with someone who is not the person you're committed to (any form, even if it doesn't include an act specifically deemed as sex itself), you are cheating. However, there are plenty of things you can do that may not fit that description but are certainly considered disrespectful to your partner. You should stop doing those things as well, or get out of the relationship.
Here is your basic guide so you never have to ask that freaking question again. Print it out. Put it in your wallet. Whatever, but do yourself a favor and put the anxiety to rest already.
1) If you have to ask yourself if something you’re doing is cheating or disrespectful, you probably shouldn't be doing it.
2) If you would not feel comfortable telling your significant other what you're doing, you probably shouldn’t be doing it.
3) If the tables were turned and your significant other were doing what you’re doing, would you be pissed? If yes, you guessed it, you probably shouldn’t be doing it.
4) If your genitals came in contact with any body part of someone who is not your significant other (aside from medical staff), that shit is straight up cheating.
5) However, if you're fantasizing about someone else but would never act on it (especially if it's someone like Mila Kunis and you don't have a snowball's shot in Hell), you're safe. We all fantasize. Anything that happens in your head and strictly stays in there is safe.
If you still aren’t sure, you’re probably in denial.
You also probably shouldn’t be in a relationship. Jussayin'.