I am currently learning Russian using Glossika and it gives the following as the translation of the sentence "I'm going out with some friends tonight. Why don't you come too?":
Мы идём гуля́ть с друзья́ми сего́дня ве́чером. Почему́ бы тебе́ не пойти́ с на́ми?
I cannot understand two things about this sentence: (1) Why is the subject of the sentence in the dative case? and (2) Why is the verb in the infinitive rather than the past tense which I was taught to use with бы constructions?