Agree the nutter was the bad bit.
Years ago I was with a hot and intelligent but complete headcase, and the relationship was extreme both ends of the spectrum. After many scrotum wrenching breakups and makeups I had enough of it, dumped her and then started shagging a lovely cuddly girl who I was mates with for a while who was into me. After a while she wanted more but I let her down gently - of course having the perfect excuse of just having been in a long term relationship, wanting nothing serious etc. Seamless transition into single batchelorness.