Do you think that if someone truly loves you, they would cheat on you? Going further, if your partner truly trusted you or believed you both had an unconditional love, a very accepting love, do you think he would have kept his bisexuality a secret?
People cheat because they cannot be honest with others, let alone themselves. And if you cannot truly be honest with yourself there is definitely no way that you can truly love yourself. And if you cannot love yourself, you cannot love anyone else. And people who cheat just do not have enough self-love to own their truths.