"Hmmm... let me throw in my two cents here..."
"Let me first say, no being on Earth is obligated or loyal to anyone that they do not want to be... I have told my girlfriend that I love her more than anything, but that is only true so long as I feel it to be so... If ever my love wanes, or I fall in love with someone else, it doesn't matter how much I love her... That's the truth of it..."
"He (hypothetically) would be more unfair to be with her and love you, if you loved him in return. Now, his method may have been distasteful, but maybe, in his heart, it was romantic. See it from his eyes, before an entire class, and even his girlfriend, he could not help himself. Even if only subconsciously, he wanted people to know."
"So, either he is a malicious person, who wanted to leave his girlfriend and used you to do it hurtfully; he is a confused romantic, who wants you and could not figure out how best to prove it; or he is a conflicted human (which makes him inherently flawed) and he loves you both and knows not what to do about it..."
"I must say, I am one who loves easily, and I am polyamorous. However, I doubt you would attempt to pursue a relationship where all three of you mutually enjoyed one another, the simple answer is that he must decide for himself who he loves more."
"It may not sound simple, but in one's heart of hearts, it's a choice any person can make with only a little difficulty. However, in turn, you and his girlfriend must accept that he belongs to no one. He will love as he pleases, and sometimes he will desire. This is one great fault I find with humans as a whole."
"What he did was kiss someone he cared about, he did not give away his love, or even risk his health or safety greatly. Should he have said something to his girlfriend first? Yes, but considering the way people treat relationships, why would he? Openness is not encouraged with monogamous love, so if he expressed an interest in you, all he would have done was caused heartache and/or anger."
"Unfortunately, you let that stuff bubble long enough, and eventually your subconscious will act..."