Should I leave or stay?

I’m currently 7 months pregnant and living with my now fiancé. But in December of last year when I was about 8 weeks pregnant he told me he cheated on me during the summer and the girl is pregnant. The other child was born in March of this year and no DNA test has been done yet but he fully intends to be in the child’s life if his. We have been in therapy for months to try to work on us and keep the relationship going but i am having a hard time getting over the infidelity and the other child and how it will affect me and my child’s future. Have I made a mistake in staying? Or should I cut my loses and raise my child on my own?