Anything subtle that creates suspicion is good. Also, don't feel bad or guilty about this. You are just providing them with some challenges to help them determine if their relationship can make it through rougher waters. You are doing them a favor!!! So definitely be a good person and help out!!!
How's that for twisting logic!!!? Hee hee!!!
One thing I've mentioned before... warm and friendly text messages when they are together... and throw in a sexy one!!! like "When are you cumming home?" Send that one this weekend. Let us know the response...
There is no arriving, ever. It is all a continual becoming.