电灯泡：the third wheel.

They are (a match made in heaven).他们真是（天生一对）。

Although they asked me to hang out after dinner, I don't want to be (the third wheel) to bother the (love birds).尽管邀请我晚饭后去游玩，但我不想做（电灯泡）打扰这对（如胶似漆的情侣）