Something that leads to another sin is a sin itself. You may think it is normal but once you start kissing you'll long for it more and more. And you'll start thinking sexual thoughts Which is a sin itself. And also demon makes sin seem normal to us. It tries to prove to us. For example about ዘፈን it might say "what's the problem of admiring God's creature?" But it really is a sin. The same goes for kissing. And also to add, in a relationship you must love God more than your partner and yourself. Someone who is faithful to God will also be faithful to his/her partner. That's my opinion.