Is it normal to want to cheat on my gf because she can't have sex?

"I've had bouts of serious depression, anxiety, frustration, irritability, and downright anger.'

If you really think it's that bad, you're losing patience, and you want to cheat, then break up with her.

Please, " I'm afraid of what it's doing to me", like what does masturbation do to you??
You obviously know exactly what your relationship with this girl is, and what it is going to be, so if you are looking for us to tell you to leave her, because you finally want to get laid, then leave her. But do not under any circumstances cheat on her. She is going to get hurt either way, but at least break it off with some dignity and respect, not with lies and cheating.

You need to have a serious talk with your girl about this problem.

Me and my gf had the same problem.
From what you wrote, it's not clear what your gf thinks about it and what she wants to do, but you two HAVE to do something. It won't resolve by itself.

Keeping that in mind, you must find some time, every now and then, to make some 'preparations'. And by that I mean that you have to introduce a finger inside her, proceed slowly following her instructions, and go back and forth to loosen it up a little bit. Repeat everyday or 3 times a week.
It won't be pleasuring for her at first, probably. But she has to endure it for your sake.
Remember that she can feel your fingernails very well, so make sure they're smooth, or wear a latex disposable glove or something like that.

When you think she can handle it, use two fingers (index and middle) and do the same.
And after that, use three fingers (index, middle, ring fingers, squeezed together to form a triangle, a triforce). This can be a bit painful for your hand, but endure it and shove all of them as deep as you can.
At this point, she should be feeling pleasure at times, if that happens continue until she's satisfied.

Three fingers' size *should* be a little less than a average penis' size, so once she gets used to them, you could try inserting your penis. If you fail, don't worry. Make her come multiple times with your three fingers and wait another day. If you fail lots of times, don't worry and keep trying. One day you'll enter, and at that point you must continue having sex until she's loosen up enough to let you insert it anytime.

If you have a big penis, since I don't think it's possible to insert four fingers (maybe two hands together? never tried), you could make her use a dildo that's a little bigger than three fingers and a little smaller than you.

My first years with my gf were sexless too, then I did all of this, and now we can have sex normally anytime we want. It's up to you two to solve the problem, good luck!

It's normal that you want that kind of relationship. Not normal that your considering cheating though. That's not right. Has she considered treatment?

http://en.wikipedia.org/wiki/Vaginismus