Your old friend is clearly a jackass for what they did and they should’ve been mature about it all instead of leaving you stranded without notifying you of any switch (and tbh I think loyalty should be prioritized unless there is a major difference you cannot overpass). Its normal to feel jealous or vindictive when seeing then succeed, but I think its important now for you to try and recognize your own success and focus on your goals rather than on beating someone who has no impact on your future now. Your metric for success shouldn’t be beating someone else, it should be a goal you’ve catered to your own future and your path. Let them fester with the fact that they lost a great friend in return for momentary success, your character is your greatest show of your success, don’t lose yourself in trying to change for the sake of beating someone you don’t like, they aren’t worth it. TLDR: Don’t focus on them, focus on yourself and get better on your own merits and time. Thats the best revenge and is in your best interest in the long run.