Dee is spot on. First of all you are safer isolating with your mum where you have already been together a few weeks. You are both safe together, plus you should look after your mum and keep her safe. You are far more likely to pick something up heading out with your friend, you don't know where he's been. Then you can bring something back and infect your mum.
We've all been exactly where you are, we made the bad decision and most of us relapsed. If we could have turned the clock back we would have 100% stayed home. Sometimes you only learn the hard way though, if you go you'll drink. A month is way too early to put yourself to the test like that.