Handy dandy excuse, eh? Anyone who has ever had a meth, crack, heroin, oxycontin, etc addict amongst their family or friends know full well, they don't just use it then stop at random (in Emily's case, used when Jonathan was away, stopped when he came home and started after he left again). There is just no way, if she was doing meth, that she just stopped when he was home. No way. She would have been off the deep end by the second or third day.
Let me tell folks what happens with these addicts, if you've never had them in your life (and consider yourself very blessed, if that is the case). They first beg or "borrow" from you, until you have nothing more to give them willingly, as in cash. When they can't get any more from you- they steal from you. They don't care that your great great grandmother left you here wedding band in her will and that it's sentimental- if it can be sold to use to buy more drugs, it's gone. Along with anything else they can steal while you're not looking. It's very hurtful, painful, and disheartening that someone you love would do this to you, they would steal to get their fix. Then, once you've caught on to them stealing and you ban them from your home, the nasty things they will say about you to not just your face as their outside screaming in your front yard, but behind your back. Some will even go as far as breaking into your home to steal more items. Some get violent. Smash and break things, threaten you.
Trust me, you don't do meth for 20 days in a row, then just stop for 10. If that was the case, if it was so easy to stop drugs like meth, there wouldn't be a country full of addicts, many who are dying daily at young ages.