Re: First time singlehanding, bad things happen, the sound of breaking fiberglass, et
Mostly my sailing these past 40 years has been solo. I occasionally still get it wrong and learn something new, so do not fuss over your one bad experience.
Re tethers: I run two webbing jacklines inboard of everything, from the pulpit, one each side of the mast, below the genoa sheets, over the cabin, inboard of the winches, to the pushpit. They are kept very taut so that they can't flop around and get under or around unwanted obstructions. The tether is kept very short - about three feet only - and at each end has those safety snap clips that require two deliberate actions to release. If you have a longer tether, just make it into a loop around the jackline with the two clips back to your harness. The idea of keeping it short means that a) you won't trip over it and b) you can't fall overboard. Because even if you are clipped on, if you go overboard at more than three knots you will probably drown. Once sailing, I NEVER go out of the cockpit without clipping on. The jacklines are tight enough to make good backrests when seated in the cockpit.
As for rough jetties and docks to leeward - I try to avoid them, but if really necessary, always use fender boards and spring lines. In the situation you described where the jetty is on a lee shore, another way out would be to put an anchor over the bow while still 30 or 40 metres off and fall back on the anchor cable (make sure the anchor is holding!), secure a stern line or two lines (one from each quarter if possible) to the pilings, by passing the line (s) around the pilings and back on board (to make letting go easier). Then when ready to depart, let go the stern line(s), retrieve to keep away from the prop and haul in the anchor while motoring very slowly ahead, with tiller or wheel centred.
Because I use all-chain rode for anchoring, in tight situations I am not too nervous about motoring right up until almost over the top of the anchor before going forward to haul it in, so as to reduce the time adrift before getting back to the cockpit. I do not clip on while anchoring or leaving as I need to be able to scamper quickly between bow and cockpit - but so close to shore, if I do go overboard it hopefully will only be an embarrassment not a disaster.