My partner for 8 years is he cheating on me?

So i been with this guy for 8 years he is the father of my child. 2 years ago my dad got very sick and i had to go and take care of him in pr. I was there for like 3 months until he passed away. When i came back home i found out my partner cheated on me mind you when i found out i also found out that i was pregnant with twins. No shit my dream twins. But me unsure of anything i decided to have an abortion. I still regret it to today. I stood with him still now recently i found out he was talking to females on fb sexting and all kinds of things. What do you guys think i should do? Is this considered cheating?? Should i just let go?