、。
I've forgotten about a two-timing woman like her, idiot.
Literal
That-kind-of two-timing woman [such-things-なんか] forgot [casual-わ], idiot.
二股かける 'to two-time / play both sides' is a relationship compound (二股 'two forks' + かける 'to put on'). なんか is the dismissive 'the likes of / something like.' ボケ is a Kansai-originated insult meaning 'idiot' — here self-directed or aimed at someone questioning him. The わ here is the masculine Kansai variant, not the feminine standard わ.