Legal options for a wife in case of an unfaithful husband

I caught my husband flirting with his neighbor on facebook messenger while we both were on our honeymoon back in 2013. At that point, he cried and asked me for another chance. He promised me he will block her everywhere and will also cut all his ties. I trusted him and continued. Again in 2019, I caught him chatting with her over whatsapp. When confronted, he first denied having contact with her & then gave up a story of being carried away by her because of the miscarriage I had early that year. Again, he cried and requested me to keep this away from his parents. He again blocked here everywhere. I gave him the last chance then. Last month on his birthday, he received a picture on his phone with the same girl wishing him a Happy Birthday. Upon confronting (this time in front of his parents), he denied having met her and claimed the picture to be photoshopped. Online forensics confirmed that the picture was real. My husband always gave me the story of not having an idea about how that girl's number gets unblocked in his phone. The reason for sending a fake picture is also not justified. For everything, he only gives one reply, 'I don't know, 'I have no idea.' I have been badly accused by his parents for suspecting him. I do not wish to stay in a marriage like this. What options do I have? On what basis can I file a divorce? Any other options apart from divorce? The only catch is I have a 10-month-old baby now and I do not wish to lose my son at any cost.