How do you get over someone who left you for someone else?

So I was with my ex fiance for 2 years not long ago he proposed to me and we were so in love, it was love I never felt before and he was so good to me even my whole family loved him and his family loved me but hated his ex's so I thought we had it pretty good.. about a month ago we split due to him leaving me out of no where saying I didn't appreciate him which isn't true. Long story short when I met him he was left with nothing and was staying on a friend's couch so I took him and his son in and supported them til he got his job.. I even gave his kids a Christmas by putting almost my whole paycheck on them so got gifts cause at the time he had no in come and no job. When he left I was completely confused to why this was happening to later find out he had been talking to a girl that I myself had met the same day he did at his friends. She ended up adding him to FB and on his birthday she messaged him saying happy birthday but I didn't think anything of it. Now when I look back on think why didn't she add me? I was their talking to her as well and clearly she was trying to get with him. His mom does not like the girl at all and he threatened to cut his mom out of his life cause of her thoughts about her (she gets old men to take her naked and half naked photos) she's got them all over her FB and in the past he's told me if I ever posted naked pictures of myself he would leave me cause he doesn't want other guys seeing my parts and it was just for him to see, so I'm extremely confused to why he would end up with someone who does what he thinks is disgusting. I also found out he recently tried to get in bed with her says after our breakup which is weird cause with me he wanted to take it slow. I am still hurting cause I did love him and did see a future with him and my daughter called him daddy since her real dad isn't around very much at all. How do I get over this? Have you ever experienced anything and how did you get over it?
How do you get over someone who left you for someone else?
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