When friendship and business mix it is natural that clarity sometimes is diminished. Don't feel badly. This type of thing is very common in the small business world and is a topic of many industrial psychology discussions.
When emotions and uncertainty come into the money picture it is highly recommended by experts in psychology and business that best practice protocols take over. Simply said, there are recommended ways to handle these types of situations, and if followed, typically result in a good outcome.
The best way to handle this is to completely separate the activities and requirements of living from the requirements of friendship. This means that rent is rent, and it is due on a certain date and certain time, no exceptions. If dog walking is something that you need, hire your friend at a rate of pay that is comparable to what you pay the back up dog walker. That way there is no rent involvement and how your friend uses that money is up to him. Make it a cash agreement if you can.
The friendship can remain as long as your friend is following the rules and honoring the boundaries that have been set.
How do you set this up? You have an honest conversation with him using a lot of "I" statements. "I feel we need to talk. I need to make sure the rent and the dog walking is separate. It is too confusing combining the two. Could you agree to X dollars for walking the dog and paying the full rent on-time by the 1st of each month...etc." This way you set up a boundary that is fixed and easier to maintain. It also lets you see if he is being faithful in his monetary commitments and sets the record clean.
For yourself, so you do not go back and forth: Ask another trusted friend or associate to hold you accountable to this agreement. You do not have to involve them in the conversation with the roommate of course, but just ask that they check in with you monthly to make sure you are not vacillating between a clear boundary and not.
Although no system is perfect, this method often resolves a great deal of monetary/friendship issues. Steven