The case of Imam Hasan al-Mujtaba (a.s.) having married a large number of women, and also excessively divorcingو is a topic that can be approached from different angles.
The claim is that Imam al-Mujtaba (a.s.) was a Mitlaaq, which means someone who excessively divorces (from the word talaq).
There are some narrations that hint to this in certain Sunni hadith books, which, for Shi'a, do not carry recognition, based on its sources and also other hadith related principles.
However, the issue is that there are some very scarce and random narrations dispersed in some Shi'a hadith books, like Sheikh al-Kulaini's al-Kafi, that do mention such a thing.
There are different views regarding this issue:
Some scholars, a number of them were Akhbaris, have defending this view, saying that because such has been stated in al-Kafi, hence it must be authentic.
Some justifications have been given that in reality is not correct and the Imam did not excessively marry, but Imam Ali (a.s.) spread this rumour to discourage people from marrying him and misusing his status.
Another view is that Imam al-Mujtaba (a.s.) wanted to increase the number of descendants of the holy Prophet (s.a.w).
However, there are many problems with accepting these narrations.
This claim is far from any reality, and nothing more than a myth. In one narration it says that a whole caravan of women had claimed that they were his ex-wives. This is very distant from the basic conduct of a normal person, let alone a Ma'soom. Divorce itself was something disliked during the pre-Islamic Jahiliyah age, and so how can we even think that the Imam (a.s.) would engage in such a thing, and so frequently.
We cannot deny the attempts made by the enemies to defame the members of Ahlul Bayt (a.s.). This being said, if there was any level of truth to this issue, why do we not have any reference of the likes of Mu'awiyah mentioning this against the Imam (a.s.).
There is a lot more than can be said about this topic, but in brief it is nothing but a myth and far from the moral and divine status of the Imam (a.s.).
For further reading, please refer to the following book which has discussed this in detail: