N2
ないわけにはいかない
Can't not, No way to avoid
いつもお世話になっている先輩の結婚式だから、行きたくなくても行かない訳にはいかない。
It's the wedding of a senior who has always been a great help to me, so even if I didn't want to go, I can't not go.
Explanation
「ないわけにはいかない」 means 'can't not do'. Social common sense, human obligation, morals or a promise bind you, so not doing it would be unreasonable: 「友人の結婚式なので、出席しないわけにはいかない」 (It's a friend's wedding, so I can't not go). The speaker may not really want to and finds it a bother, but as an adult has to do it anyway. The subject is mostly 'I', and it is common for weddings, funerals and visiting the sick.
Mixed up with
「ないわけにはいかない」: bound by social ties, morals or face; it would be wrong not to.
「ざるを得ない」: circumstances leave no other choice, so you do it against your will; written.
「ねばならない」: a formal written 'must'; duty and rules.
「なければならない」: the everyday, objective 'must'.