Help!! Need some advice!!

Hey ladies,

So i could really use some advice. Im going threw one the most difficult times in my life. This past February my mom became very ill very quickly. She was rushed to the hospital. Long story short her cancer had returned. I quit my job to care for her. She passed march 24th. I was devastated. Im my mothers only daughter and youngest by many yrs. i was basically an only child. A little over a month ago i started to see that my fiancé (proposed on January) had been acting distant and just hiding things. I eventually found out that he had been talking to a girl he worked with. She was completely honest with me told me everything. He didnt. So then i started digging around his phone records and found more girls. He claims he only talked to them. And i cant prove anything more. Ive contacted the girls that would actually answer me. He lied to them told them we werent together told them lies about me to make him out to be a victim. He claimed i was disconnected and depressed. But i feel like its so wrong. My mom was dieing and i was beside myself. After 6 yrs and a 4 yr old son together and we were supposed to get married in july a small wedding. Obviously it didnt happen due to circumstances. I love him with everything i have. But now i feel like im

Not good enough. Im not attractive enough. Im blaming myself. Ive been starving myself. I dont feel comfortable in my own skin. Im smarter then this. Its a constant battle everyday between what my brain tells me and what my heart feels. Part of me wants to believe him because i was so depressed. But my mom my best friend died suddenly and in a devastating way. I feel like an asshole if i stay with him. Any advice ladies? I would appreciate all opinions because i have such mixed feelings. If he was lonely why not talk to male friends. Why talk to females y lie about me and make it like im so horrible and hes stuck. Our sex life is different. Hes just not the same. Im so confused. Help!!