I have touched on this in previous answers so apologies for a bit of repetition here. Bassanio is an odd mixture. On the one hand he seems pleasant and affable, if possibly a bit bland, and he would appear not to share the anti-semitism that his friends, including Antonio, indulge in. He is also protective of and loyal to Antonio, urging him not to enter the dangerous bond in the first place and then showing support when Antonio finds himself in deep trouble. On the other hand it is hard to avoid the conclusion that Bassanio is a bit of a waster and chancer, part of the group of seemingly idle young men-about-town who gather round the rich Antonio. Bassanio is already in Antonio's debt and is now coming to ask for a good deal more money to risk in what is essentially a pure gamble. His purpose is to secure the hand of a rich lady and thus - as I read it at any rate - his high-spending lifestyle. His very first mention of Portia refers to her wealth, so there is no mistaking his primary motive in heading for Belmont. Viewed in this light his conduct leaves him little short of a con man, albeit one with attractive redeeming qualities. Any time I have watched the play or read the text I've always found myself wondering whether to like or loathe him and I always end up somewhere in between.
I agree with Anzio, Bassanio is wooing Portia to get her money to be able to live an easy life and to pay back the money he borrowed (with precious little hope of repaying) from Antonio.
Bassanio is a foppish bankrupt aristocrat. The only thing he owns of value is his family name. He obviously thinks he deserves a rich and comfortable life and, because he can't afford one, he lives in off others, stacking debt.
Is he poncing off Antonio? Is he knowingly using his youth and good looks to get money out of a sad, rich, lonely, old homosexual? I think you can certainly read it that way.
So he is not a very moral person, but he's not a deliberately bad person. He's not malicious or wicked. I think he's just a weak, careless character who likes parties and palaces but doesn't want to work for them or think about consequences or responsibilty. I don't think he intends to hurt anyone. BUT, in the end, he drags Antonio into a very dangerous, serious situation.
Basically, he gets very very lucky and 'wins' a vast fortune belonging to his new wife. If Bassanio hadn't won Portia, he'd have probably ended up in court for debts and bankrupty at some point. He'd probably have ended up old and homeless or locked in debtor's prison.
I think I like Bassanio, but I don't in any way admire him. He's a nice guy, but he's not a good one.