As a Newbie Photographer, I'd have to go with "spur of the moment" for the answer when dealing with kisses. Kisses always look weird to me if the two models have no attachment to themselves, or its just "another silly request". The perfect kissing picture is going to include emotion, and something intense or even passionate. So, if you plan to do some with your boyfriend, just let it be spontaneous or find the perfect moment to do it and let the photographer do their best in capturing it. It's hard to explain, but what I find is that looking through such pictures helps, like for me these:
Just a few examples of good references for "kiss" scenes, and i'll add like Skuggi angle helps shots as well, namely if you have no access to editing software.