Advice

I was in a relationship with my ex for just over 2 years. He was absolutely my best friend. I lost my virginity to him after our 1 year, we were sure to spend forever together. Everyone thought so. Around our 23 month mark he started helping this family (who has a daughter a year younger than me) with their truck and he would hang out with the dad a lot. I trusted him cause he told me he loved me and everything seemed normal (he would still talk about "our" future house and family and stuff) but about a week before our anniversary he got really protective of his phone and then a day after our anniversary someone told me they seen him with the daughter at a store. I asked him about it and he said he took her there cause their family doesn't have a car and I believed him. Then he broke up with me through a letter on New Year's eve(9 days later).  He said I was too immature for him and that he needed to get closer with God and that he didn't have any outside temptations. But 2 days later there was a picture of him shirtless with the daughter in his ice house. And he's stopped coming to church and now they are official. He's doing all these things for her that I asked for but he always said he's "not that type of guy".  I guess I don't know what I need advice on here but I really could hear some opinions on the subject so I know I'm not crazy for feeling the way I do.