Well he and Miles were friends (are they still I wonder given the sudden departure?) and friendship is important. But I seriously hope it doesn't have more than an immediate effect and we don't know that it was the break up with Kim that adversely affected his tennis during that period do we?
The parallel with Kim hadn't escaped me, but, given what we know now about Team Murray, I've a feeling that this has been going on for quite a while and, in fact, it may well have been this, as well as the fall-out from the AO, which impacted negatively on his tennis for so long.
By Andy's admission, Kim and he had been back together "for longer than anyone knew". That being so, then they were together when he was still playing poor tennis. Anyway there's a big difference between the break-up of a long-term emotional relationship and what you might call a close "working friendship". At least Andy now has the support of Kim (and Maggie) to sustain him.