Hi, Ben —
An individual's culpability is really the Lord's business, but let's just say it can be serious; it can harbor lust, objectifying others (mentally) as objects for sexual gratification and other ill effects.
It is our fallen nature that leads to these distortions of our sexuality. It is better to avoid it, but people do fall, so seek reconciliation and move on.
A solid prayer life can make the urge not so overwhelming and makes chastity doable.