First, let’s look at the broader context of the Mary/Joseph relationship. Church tradition maintains that Mary was a virgin at the time of the conception of Jesus, and that she remained a virgin her entire life, never having sex with Joseph. This belief is reflected in numerous early Church writings and can be found in the apocryphal Protoevangelium of James, as well as in the writings of Church fathers like Augustine.
So if Mary and Joseph never had sex, did they ever even kiss? It’s a great question, but the teaching of the Church doesn’t get that specific. Some Catholics might interpret Mary’s perpetual virginity to mean that they probably avoided kissing altogether, while other Catholics might argue that kissing was a way that Mary and Joseph could show their mutual affection without having intercourse. In the end, we’ll just have to live with the ambiguity.