Should i stay?

My boyfriend of 20 years has cheated twice that i know of through the course of the relationship. The first time I forgave him and now he wants forgiveness again but i feel like its nothing left because if i meant so much he wouldnt have cheated at all or to be fair cheated a second time. I think i should let go but before then i wanted advice. Also we share a house together and have 3 kids.