<human>: Okay so here is my situation: this guy and i have been dating for 6 months, and i just recently found out that he gives his mom a peck on the lips as a goodbye thing. I understand that in some cultures, this is a norm, but for me this is the weirdest thing ever for a multitude of reasons. 

Firstly, the woman is with someone. Transmission of STI is possible from mouth to mouth contact now.

Second, he went around the issue when it was brought up (very gently)  saying that he only does it on the cheek or side of mouth; and when stating that id seen this done in front of me, he finally admitted to it, so obviously it must be embarrassing for him.

Thirdly, he has stated that he one time left without doing it, and the mother guilted him saying "oh you dont want to give your mother a kiss?"

My whole point being, i dont feel very comfortable kissing him anymore, especially due to the potential sti transmission, but also just the weirdness of the whole situation as he is too old IMO to be doing this. How do i bring this up to him?

Give me a shortened version of the text
<bot>: BF pecks mother on lips, how do i bring this up? Dont want STI, also feel there may be an underlying issue with her losing her husband a long time ago, and thats why its never stopped.