the use of ὅστις chariton 1.2.5

[daivid]

Ἐπαγγέλλομαι διαλύσειν τὸν γάμον: ἐφοπλιῶ γὰρ αὐτῷ ζηλοτυπίαν, ἥτις σύμμαχον λαβοῦσα τὸν ἔρωτα μέγα τι κακὸν διαπράξεται.’
Most of this is straight forward but I don't see why Chariton used ἥτις rather than plane ἥ. Is it because there is no definite article in front of ζηλοτυπίαν?

Just in case I don't understand the rest as well as I think, here is my translation:
I announce that I will dissolve the marriage, For I will arm against it jealousy which will take an ally desire, a great evil to produce.

[jeidsath]

Sidgwick mentions that ὅς or ὅστις with the future indicative can indicate purpose.

δέομαι ἄλλου τινὸς λόγου ὅς με πείσει. I need another argument to convince me.

[Hylander]

jeidsath is correct--this conveys purpose. But to capture the generalizing function of ἥτις, as opposed to simple ἥ, you might translate "I will arm against it a jealousy such as to to . . . do it a great evil.

[mwh]

daivid you haven’t quite understood the clause. ἥτις σύμμαχον λαβοῦσα τὸν ἔρωτα μέγα τι κακὸν διαπράξεται lit. “which [or “who”, personifying the armed Ζηλοτυπία] having taken Eros as ally will accomplish a big evil” i.e. “who by taking Eros as her ally will create a huge disaster.” διαπράξεται is the main verb of the relative clause, and the participle λαβοῦσα is subordinate to it: you seem to have misconstrued it.
You might describe Donald Trump as someone ὅστις συμμάχους λαβὼν τοὺς ἀνοήτους μέγα τι κακὸν διαπράξεται.

[polemistes]

You might describe Donald Trump as someone ὅστις συμμάχους λαβὼν τοὺς ἀνοήτους μέγα τι κακὸν διαπράξεται.

Off topic:This might be the most accurate description of Donald Trump so far. But it is ironic that it's in Ancient Greek so none of his σύμμαχοι will be persuaded to change their alliance.

[daivid]

jeidsath is correct--this conveys purpose. But to capture the generalizing function of ἥτις, as opposed to simple ἥ, you might translate "I will arm against it a jealousy such as to to . . . do it a great evil.

That is a fairly subtle distinction that in English we don't usually bother to make so it is no wonder that ὅστις gives me problems. Your help is much appreciated as is that of mwh and jeidsath.