You can LOVE someone and cheat on them, but you can't be IN LOVE with someone and cheat.
When you are IN LOVE with someone they are providing everything you need on an intimate level - psychologically, physically and spiritually. They're the whole package. When you're in love with someone no one else matters on that level like that person does.
You cannot cheat on someone and be in love with them, even if you feel guilty afterwards. As long as you're cheating, it's just a strong love IF THAT...not IN LOVE. Something wasn't being provided for you on an intimate level that you felt you needed to go get. The person you think youre "IN LOVE" with was LACKING. Truely being in LOVE is a entirely encompassing feeling. No holes are gaps exist when you are IN LOVE. Are they perfect? No, but they cover ALL the bases.
The strongest loves one can have in life are for God, their parents, their children, a sibling and your significant other.
A true best friend or extremely close cousin will essentially fill the role of a sibling...hence the saying "He/she is like a brother/sister to me."
A pet can fill the role of a child as well, and a guardian who plays the role of a parent can substitute for a parent, but those 5 loves are the strongest.