Sun Shine, frustration and sadness can be too dangerous in some time. do not stay alone for some time, until you develop some hopes in your life again. better to stop thinking about him or your past. talk to your friends or relatives for hours, get you engaged in some work or talks, or go to your friend's or relatives house to stay with her/them. I heard that one very effective way of releasing stress or tension is to say - i hate you, i hate you , i hate you;  put your pillow in your lap, say it loudly two three times, and throw the pillow out to a corner of your room, or do something like that way. if you find someone who was also betrayed by his/her spouse or gf/bf, talk to her or him, he/she will hear your griefs honestly.

you need to judge him from his actions or behaviours (if he also felt that you two would be a perfect couple, why he went for another girl?), not from what he says or said - "you are so cute, beautiful, etc???". you honestly loved him, but he did showy love to get something, eg, your friendship or whatever, from you. no doubt, he has betrayed you. so there is no point of still feeling for him. cherishing your happy moments with him in the  past can be harmful as it may make you feel that you are missing him very very badly.

Try to watch funny classic movie or comedy shows - Golmal, Andaj Appna Appna, Dhamal, American wedding, or Russell Peters, comedy TV shows, eg late night show, or Nepali or Hindi comedy shows or serials. there are so many movies that you can watch online. do not listen and watch sad songs. sadness may apply to your life, but sad songs do not help you heal your wounds, listening them just make you sad. try to laugh as much as possible.