I know it is one of the worst pains imaginable, but you have to think about yourself now.
Work out, get busy, do what you love to do without feeling that you need anyone else.

She's a person who did something wrong to you, now forgive her and let her go. Don't put her or anyone on a pedestel, by allowing yourself to dwell on the situation. It happened, you can't do anything about it. She chose to do what she wanted to do without any regard for you, now let her live with that selfishness. Don't ask her back, don't write her or contact her in any way. As hard as it is, you have to just try to eliminate those feelings by forgiving her and being that good person.
And, Don't EVER GO BACK!!

Read my story if you want my fiancé cheated on me as well but she dumped me, go no contact forget scum like that and every day you will feel little better.

Remember it's her not you.

Distance yourself from her asap, and so you can rest, sleep well and then think- take your time with your thoughts and action and Be sure you do what is right FOR YOU only.

I think she is v selfish and thoughless on how she can cheat and when she realises how she will loose you comes running back, sending lots of texts- does she realise what pain she is putting you thru- NO.

Did her ex dump her-this might explain why she went back to him-anyway, it sucks-i know-but think what it would be like if you were still with her. She lied and cheated on numerous occasions-that says nothing about you, and a lot about her. She just doesn't seem like a very good person. You definitely are better off, whether you realize it yet or not.