Hi MJ
Been through a similar situation. Not so much the receiving of dirty messages, but the dating websites and escort services were used by my ex when taking cocaine.
I also found out that he cheated. Not saying your partner has as everyone is different. However, I was with my ex from the age of 15 (17 years together, 3 kids) he had never showed / displayed any tenancies to cheat on me. He was a loyal honest person. When the drugs completely took a hold and he was using more or less every week for a few days in a row. Sometimes he even disappeared for a week or more. He completely changed and became an unfaithful, deceitful lier. I’m not saying your partner is this person, but I can say you can not trust him and there is a possibility he will cheat. Its a seady drug. I found that the filth was never used with me but must have been with others. He kept our sex life different to his cocaine one.
Keep ya chin up