is my English grammar, right?
No, the correct preposition should be to, not on. In other words, the sentence should be:
“Thank you for being like a dad to me.”
The sentence looks great apart from your choice of the preposition ‘on’. The correct preposition in this sentence is ‘to’ so ‘thank you for being like a father to me’. ‘To’ is used to show the connection between you and the father figure.
When we use the preposition ‘on’ it usually suggests that there is some type of physical contact between two things. For example, if a cat is on the table this means that the cat is sitting or lying on the table and there is physical contact between the cat and the table.
