All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
If this man is, as you mentioned in the question, religious and has a good moral character, then it is advisable for you to marry him. Being a third wife or thinking that you will be jealous is not an obstacle for marriage neither in a religious point of view nor in regard to customs.
The Prophet married many wives and it happened sometimes that they were jealous between themselves.
It might be that there are some religious benefits in such a marriage would help the woman overlook and disregard such matters. Therefore, it is very important that you perform the Istikhaarah prayer; for more benefit on how to perform the Istikhaarah prayer, please refer to Fatwa 81434.
As regards your father, first you should seek the help of Allaah in trying to convince him, and then the help of some knowledgeable people and those who are very close to him. Then, if he agrees for you to marry that man, all perfect praise be to Allaah, but if he refuses and provides you with an acceptable religious reason, you are obliged to obey him, as you are obliged to obey your father in what is permissible while on the other hand you are not obliged to marry this specific man.
Finally, it should be noted that if it happens after performing the Istikhaarah prayer that you are not married to him, it might be that Allaah repelled harm from, and He may facilitate for you another husband who is better than him. Allaah Says (what means): {But perhaps you hate a thing and it is good for you; and perhaps you love a thing and it is bad for you. And Allaah Knows, while you know not.}[Quran 2:216].
Allaah Knows best.