Bear in mind: not every person is a person you want to spend time with. When you first meet someone, that's often apparent, right off the bat! Maybe there is something about their manner that doesn't make you feel comfortable, or maybe you simply feel no rapport. Or for any or no reason at all - you don't find their company to be pleasant. Well, there's nothing insulting there. It's a simple matter of interpersonal chemistry. It works itself out quite naturally: you simply choose not to end up spending very much of your time on that person.
You're under no obligation to spend your time with people, especially if you find it not pleasant to do so. "Your time," of course, not meaning work time or school time, but whatever time you are free to set for yourself. Your discretionary time. Your time.
And as I've said, when there's zero rapport, when there's absolutely no reason to spend that time, it's commonly apparent right off!
But sometimes, it isn't. Sometimes there is rapport, and then the rapport breaks, or fades, or is otherwise gone. The reason isn't necessarily germane. If there is no shared stake, no responsibility undertaken and held in common, no overriding reason why you two must interact (at a level that would then become, essentially, a work relationship), then why would you interact? If we are talking about a simple relationship, a friendship or acquaintanceship between two people whose basis for interaction has been the most natural, common, blessed and desirable basis there is: you are both enjoying the interaction - well, naturally if that basis goes away, if the interaction can no be longer a pleasant thing for you, then that's more-or-less that. There is no more reason to spend time with that person whose presence in your life is not pleasant, than with a person you just met whose presence in your life is not pleasant. You don't want to spend unpleasant time with a person, if you don't have to - whether you're just getting to know them, or whether you suddenly just got to know them, a little too well.
Remember: "forgive and forget" always applies. But depending on that underlying interpersonal chemistry, it applies differently. If someone wrongs you in some way, but there is still rapport, and they remain a person you want to spend time on, then of course by all means, forgive and forget. And spend the time!
But if the rapport is gone - not based on any action of theirs, but based on the person they are! Based on who they are, who you know they are. Maybe you know them a little better than you did before, and as it turns out, they are not a person with whom spending time can be pleasant for you. Well in that situation, you still must forgive! If there's anything at all to forgive - and if you're being honest with yourself, there usually isn't. Usually the other person has done nothing wrong, they were just being who they are. You may have been angered, or hurt, that who they are is not what you thought or wanted, but that's not their fault. And even if something is their fault - even if they done you wrong: always, always forgive. Even if only for your own sake, forgive! And you still should forget. Just for your own sake. You have no need to carry a grudge. Let it go, let it drop. It's a burden that can't help you on your road; let it go.
Forgiveness doesn't mean you choose to spend your time on someone whose company is not pleasant to you. Someone with whom, if you'd known them a little better up front, you would never have elected to spend the time in the first place. It makes very little sense to perpetuate a relationship like that! In fact, such behavior is cruel. It is dishonest and more than a little heartless, to the person whose company you are merely tolerating. Don't flatter yourself: no one wants that from you. No one wants to inflict their odious presence upon someone who is merely putting up with them. It is in these cases that forgive and forget applies, but with a slight variant.
For those people you actually want to spend time with: forgive and forget.
For the people you don't: forgive and forget it.