How do you tell someone that you're in a sexual relationship with that u have an std, which is manageable? Will he stay with me? How to I deal with Herpes and Dating? Should I tell anyone at all or pretend I don't know?

Will he stay with you? That is a question we can't answer. Some men will yet others won't.

Should you you tell him? Yes, if you are sexually active with him you are obligated to tell him.

You should tell him before, you are sexually active. If he will stay? That is up to the man and how your relationship is.

I agree, he should know BEFORE you get anywhere near being sexually active together... in many places you could and should be held civilly liable if you failed to disclose it because there is no cure.

If they stick around or not is up to the individual.

When you get to the date where you both think you might want to hop into bed on the next date, you tell him.
Sure, it isn't easy to find that moment. Either jumping the gun or waiting til he thinks you are springing it on him too late.

As for 'management' of herpes when you are sexually active, what do you plan to say?

How about the following...

"Bob, I have to let you know that I have herpes. This STD is managed with medication and is typically not spread unless I have an outbreak. However, for your sexual health it is best that you wear a condom every time we have sex, whether I am having an outbreak or not."

After that it is his decision whether to stay with you. Some men will, others won't.

Before starting with any new partner there has to be a series of conversations that include the following topics:
1). STD state. Hiv, Aids, Herpes, HPV,
2). Birthcontrol.
3). If pregnancy occurs what happens?
4). Limits & kinks. Oral, anal, vaginal, BDSM,
5). Exclusivity. Mono, Poly, swingers...

This will open up conversations that will strengthen the relationship. If you can't talk about it, you shouldn't be doing it.