Interesting. Doesn't look like impact damage. I think your guess about the click from the last six months is likely correct. My titanium frame failures have manifested themselves exactly as that.
I'd get a new bike/frame personally. I think titanium is far from the lifelong frame material it's made out to be. Maybe it could be, but I suspect few builders have the experience to build a titanium frame which gives it that special ride feel and make it long lasting. Yes, I know some of you have 30+ year old titanium frames, but I doubt many of you are riding them daily.
I had a titanium frame failure on a weld fixed, and it simply failed elsewhere within a year. If you feel really attached to it, maybe get it fixed and use it for light work.