David wrote this Psalm after being betrayed by his son (2 Sam 15). Betrayal has not changed since then. Once upon a time I was new to a certain group, and after a time I discovered that one of my new friends had spread some hurtful words about me. It was heartbreaking because this was someone who had welcomed me and whom I had trusted.
The God of love calls us to trust (1 Cor 13:7) even though we are sometimes betrayed, and when we are, God promises that vengeance is his alone so we may repay evil with good (Rom 12:19&20). Sometimes we are the ones who fail and betray; when we fail ourselves, our friends and our God, God offers us an unconditional love to heal the hurt we've caused.
if we are faithless, he [God] remains faithful, for he cannot disown himself -2 Timothy 2:13