Just not the same mentally since he was caught cheating on Jelena.
The same happened to Manny Pacquiao and Tiger Woods. They were destroying their opponents physically and mentally. Had that extra it factor to them and arrogance. Pacquiao was gambling, drinking, cheating on his wife and got caught. Did this born again Christian thing and starts losing matches. Tiger got caught, was revealed he had a mistress in every city he toured in. Can't hit short putts to save his life. The same putts he used to sink and put fear into the guys on the top of the leaderboard that he was roaring his way back. I think the egos of all 3 came crashing down... coincidentally enough once Tiger and Manny got caught, lost their dominance, and started the "rehab" process they both kept saying "I'm focused on my family right now, insert sport name comes second right now to my family". Same stuff Nole's been saying.
Nole's repeating the same pattern. Tiger's been battling "injuries" for years since the affair news went public. Pacquiao has been beating up mid-card opponents but lost winnable matches. Nole hasn't won a tournament of any major importance since Roland Garros (maybe Toronto but after olympics really nobody played there. That was his to lose with that field).
I think what the issue is, these guys were all at the top of their games at the top of their sport. They had that extra arrogance and ego boost being the best at what they do. They have all this testosterone, sleeping with any woman they'd like really. They get caught and then their egos come crashing down and they lost that mental edge they had that got them to the top and allowed them to commit all this infidelity. Novak has no confidence right now and it shows. It's effecting his work ethic, his training, his mental stamina, etc. There's a reason Boris said he dropped Nole because Nole just wasn't practicing with the same intensity as before. It has zero to do with wanting to spend more time with Jelena and Stefan and more to do with him trying to mend the marriage without public embarrassment. Nole makes more than enough money to fly his entire family out to every tournament he wishes (like Roger does with Mirka, parents, all the kids, etc).