The thread convolves faith--sets of beliefs that are not amenable to scientific verification -- and teachings, which can include sets of expected behaviors. Such convolution has been with us since the beginning of religion, which of course combines faith and teachings.
The teachings have typically been used to guide (read:control) the behaviors of the faithful. The control often breaks down--example Catholics and contraception--when there is an inconsistency between reality and teaching.
Controlling sexuality has been part of the teaching for many if not most major religions. It doesn't work. Example--Catholic clergy. Swinging is an accommodation that respects the institution of marriage while allowing for sexual variety. Swinging need never challenge faith, it inevitably challenges teaching.
What matters is how swinging affects your/your partner's life views. Divorcing monogamy from commitment (how's that for a brain twister) requires rejection of teaching but may in fact support your faith. If you wake up in the morning, embrace your partner, and say with meaning "I love you more than anyone else in the world", what else matters?