How to forgive a cheater

How do you forgive them and keep trying to make it work without thinking about it? We could be having the best day of our lives and that's all I can think about like you say you love me you say you only want me yet your messaging other women and doing god knows what and has done got knows what. I want to move on I do love him but it's so hard I have never stepped out of line in almost 8 years.but he keeps doing it and it's always my fault or depression made him do it 🙄 ( we lost our son sadly to a birth defect and that was his excuse)

I should be married to him have my own place with kids at least 2 cars and a happy life 😮‍💨 but I can't because honestly I am scared to because of him constantly stepping out on me 😮‍💨 it's like almost every year he steps out on me and I I don't want to leave him but I can't not think about it.

Is there anything I can do besides leave him? I know honestly that's probably what I need to do but idk if anyone will be able to understand what I have been through and except me. If that makes sense.