My friend kissing my man for new year!

I have been so unlucky in Love. I am not a beautiful woman to be honest and i have had only tow relationship in my life. I am now 41 years old. I met this guy at a church service which i hardly go to that church but just by the grace i went and we saw each other with this man i have now been dating for two years. We were going to get married in August this year but over christmas, we went to a new year dinner at a friends house. One of my friends went out to her car and then my man went missing too. I just wondered where he had gone for about 30 minutes especially when everyone was now shouting happy new year but when i went to the car, oooh my God, they were there kissing and they both were shocked. They told me its the first time and i should forgive because they were just celebrating new year. He still want to marry me but how can i? If i dont who will ever marry me? i want a kid, even one, i am so depressed, betrayed and i am really hating the fact that i cannot even keep a man. Please its only 2nd of January but