I personally think that, whatever fleeting happiness the text seems to promise Bassanio and Portia, that long term happiness will be impossible for them to attain. Let me explain my reasoning. Firstly, let us remember that Bassanio is a singularly unimpressive character. He openly admits the way that he is a spendthrift and a rather prodigal character when we first see him before going on to deliberately manipulate Antonio and his love for Bassanio so that he can gain more money, even though this will place Antonio in a very fragile and precarious position. When he speaks of marrying Portia, it is her wealth that he is after, and although we could argue that he later on falls in love with her as a person, at the same time his motives for going to Belmont are purely pecuniary.
In comparison, let us consider Portia. Not only is she beautiful, but she is also extremely intelligent and clever. Let us remember that while Bassanio was watching helpless as Shylock was going to carve his pound of flesh from Antonio, it is Portia who comes up with the strategy to save her husband's friend. It is her who shows the necessary ingenuity to find the legal loophole that will save him and condemn Shylock and it is her who is able to trick her husband and the other male characters. This makes me think that the union between Bassanio and Portia is one of two unequal characters, with one possessing all the charm, grace, wit and intelligence that the other so sorely lacks. I don't predict a happily-ever-after ending for them, therefore.