Just tell the truth.
Let's take a real example.
My husband reached a stage when he stank so bad that I couldn't bear to be in bed with him.
I said, "Honey, I have something really difficult that I need to say, and I'm afraid you won't want to hear it."
He took a huge sigh and said, "Okay, I'm prepared now. Tell me."
- "Well, you know how I've been sleeping on the couch for the last nine months and you keep wanting me to come back to bed?"
- "Yes."
- "It's because there's been a change in your smell. You smell like an old man in a nursing home."
- "I don't believe it!"
- "I'm sorry, sweetheart, but it's true. I think it might be something to do with a drop in testosterone, but I think the main thing is hygiene. And I don't think you can smell yourself because you're so used to it."
- "Well what can I do about it?"
- "I'd like you to wash your pillow slip once a week, shower before bed and wash your hair, only wear freshly washed tee-shirts, and wash your clothes once a week."
- "Okay. I'm willing to give it a try."
He kept his word the same day.
That night I returned to the bed, he's kept clean since then.
He's happier, and I'm getting much better sleep.