Forego originally meant “go or come before,” as in “Salad foregoes the main course.” But now this usage is out of fashion, although still acceptable. The only time forego is commonly used with this meaning today is in the phrase foregone conclusion, which means “a conclusion already expected or known before any discussion or investigation.” And just in case you do use forego with its old meaning, take note that the past tense is forewent (foregone is the past participle).
Almost nobody uses forego with its old meaning, “go before,” anymore; rather, it is more often used as an alternative spelling of forgo.
Forgo is a commonly used verb meaning “to refrain from or do without something”:
I will forgo dessert because I am on a diet.
Unlike forbear, which can be used intransitively (without an object), forgo can only be used transitively—only with an object, which can be a noun, as shown above, or a verb, in its -ing form:
Many days I forgo eating breakfast.
Finally, remember that, since forego has gone out of style, it is not uncommon for people to spell forgo as forego. But you can remember the difference between these verbs by noting that fore means before.